Add comprehensive category import/export with cherry-picking and default categories

Features added:
- Category import/export with selection dialogs and checkboxes
- Cherry-pick specific categories for import/export
- Default categories loaded from default_categories.json on first run
- Enhanced Import Data tab with scrollable instructions and new user guidance
- Comprehensive documentation in CATEGORY_IMPORT_EXPORT_GUIDE.md
- Sample categories file for reference

Database changes:
- Add export_categories_to_dict() and import_categories_from_dict() methods
- Support for updating existing categories or skipping duplicates
- Flexible JSON format support (with/without metadata)

GUI improvements:
- Category selection dialogs with Select All/Deselect All buttons
- Pattern preview for each category in selection dialogs
- Increased dialog sizes and added scrollbars for better UX
- Enhanced Import Data tab with 30-90 day recommendation for new users
- Better button sizing to prevent text cutoff

Documentation:
- Complete guide for category import/export functionality
- Examples and use cases for cherry-picking categories
- Default categories documentation and customization guide

Author: bsanders1979

CATEGORY_IMPORT_EXPORT_GUIDE.md

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+# Category Import/Export Guide
+
+## Overview
+
+The Transaction Manager now supports **importing and exporting categories** as JSON files. This allows you to:
+- Backup your category rules
+- Share categories with other users
+- Migrate categories between databases
+- Version control your category configurations
+
+## How to Use
+
+### Exporting Categories
+
+1. Go to the **🏷️ Manage Categories** tab
+2. Click the **📤 Export Categories** button
+3. **Select which categories to export** using the checkboxes
+   - Use **Select All** to choose all categories
+   - Use **Deselect All** to clear all selections
+   - Manually check/uncheck individual categories as needed
+4. Click **Export Selected**
+5. Choose a location and filename for the export file (default: `categories_export_YYYYMMDD.json`)
+6. Click **Save**
+
+✓ Only your selected categories will be exported to a JSON file with metadata
+
+### Importing Categories
+
+1. Go to the **🏷️ Manage Categories** tab
+2. Click the **📥 Import Categories** button
+3. Select a JSON file containing exported categories
+4. **Select which categories to import** using the checkboxes
+   - Use **Select All** to choose all categories from the file
+   - Use **Deselect All** to clear all selections
+   - Manually check/uncheck individual categories as needed
+   - Each category shows its pattern type and pattern for reference
+5. Choose import options:
+   - ☐ **Update existing categories** - If checked, categories with the same name will be updated with new patterns
+   - If unchecked, duplicate category names will be skipped
+6. Click **Import Selected**
+7. After import, you'll be prompted to **Recategorize All Transactions** to apply the new rules
+
+## Export File Format
+
+The exported JSON file contains:
+
+```json
+{
+  "version": "1.0",
+  "exported_at": "2025-10-15T12:00:00.000000",
+  "category_count": 5,
+  "categories": [
+    {
+      "name": "Amazon",
+      "pattern": "AMAZON",
+      "pattern_type": "contains",
+      "description": "Amazon purchases",
+      "color": "#FF9900"
+    },
+    ...
+  ]
+}
+```
+
+### Field Descriptions
+
+- **version**: Export format version (for compatibility)
+- **exported_at**: Timestamp when the export was created
+- **category_count**: Number of categories in the file
+- **categories**: Array of category objects
+
+### Category Object Fields
+
+| Field | Required | Description | Example |
+|-------|----------|-------------|---------|
+| `name` | ✓ | Category name (must be unique) | "Amazon" |
+| `pattern` | ✓ | Pattern to match in transaction descriptions | "AMAZON MKTPL" |
+| `pattern_type` | ✓ | Type of pattern matching | "contains", "regex", "startswith", "endswith", "exact" |
+| `description` |  | Optional description | "Amazon marketplace purchases" |
+| `color` |  | Optional hex color code | "#FF9900" |
+
+## Pattern Types
+
+### contains (most common)
+Matches if the pattern appears anywhere in the transaction description (case-insensitive).
+
+**Example:**
+```json
+{
+  "name": "Amazon",
+  "pattern": "AMAZON",
+  "pattern_type": "contains"
+}
+```
+Matches: "AMAZON MKTPL", "Amazon.com", "Purchase from Amazon"
+
+### regex (powerful)
+Uses regular expressions for complex matching.
+
+**Example:**
+```json
+{
+  "name": "Gas Stations",
+  "pattern": "SHELL|CHEVRON|ARCO|76",
+  "pattern_type": "regex"
+}
+```
+Matches: "SHELL GAS", "CHEVRON STATION", "ARCO #123", "76 STATION"
+
+### startswith
+Matches if the description starts with the pattern.
+
+**Example:**
+```json
+{
+  "name": "Apple Services",
+  "pattern": "APPLE.COM",
+  "pattern_type": "startswith"
+}
+```
+Matches: "APPLE.COM/BILL", "APPLE.COM iTunes"
+
+### endswith
+Matches if the description ends with the pattern.
+
+### exact
+Matches only if the description exactly equals the pattern (case-insensitive).
+
+## Cherry-Picking Categories
+
+Both import and export support **cherry-picking** - selecting only specific categories you want to work with.
+
+### When to Use Cherry-Picking
+
+**Export Specific Categories:**
+- Share only relevant categories with someone (e.g., only business categories, not personal ones)
+- Create focused category sets for specific purposes
+- Export only tested/finalized categories, excluding experimental ones
+- Backup specific category groups separately
+
+**Import Specific Categories:**
+- Import only categories you need from a larger set
+- Avoid importing categories that conflict with your current setup
+- Test new categories one at a time
+- Selectively merge category sets from different sources
+
+### How Cherry-Picking Works
+
+1. **Export Dialog:**
+   - Shows all your current categories with checkboxes
+   - All categories are selected by default
+   - Deselect categories you don't want to export
+   - Only checked categories are saved to the JSON file
+
+2. **Import Dialog:**
+   - Shows all categories found in the import file with checkboxes
+   - All categories are selected by default
+   - Deselect categories you don't want to import
+   - Only checked categories are processed
+
+### Examples
+
+**Example 1: Share Business Categories Only**
+```
+1. Click Export Categories
+2. Click "Deselect All"
+3. Manually check only business-related categories:
+   ☑ Office Supplies
+   ☑ Business Travel
+   ☑ Client Meals
+   ☐ Personal Shopping (leave unchecked)
+   ☐ Family Dining (leave unchecked)
+4. Export → share with business partner
+```
+
+**Example 2: Test New Categories Individually**
+```
+1. Receive a categories file with 20 new categories
+2. Click Import Categories
+3. Click "Deselect All"
+4. Check only 1 category to test:
+   ☑ Streaming Services
+5. Import → Recategorize All → Review results
+6. If good, repeat for other categories
+```
+
+**Example 3: Merge Without Duplicates**
+```
+1. Import a categories file
+2. Review the list - some already exist
+3. Uncheck categories you already have:
+   ☐ Amazon (already have this)
+   ☐ Groceries (already have this)
+   ☑ Gas Stations (new - keep checked)
+   ☑ Utilities (new - keep checked)
+4. Import Selected
+```
+
+## Use Cases
+
+### 1. Backup Categories Before Making Changes
+
+Before making major changes to your category rules:
+1. Export your current categories
+2. Save the file with a descriptive name (e.g., `categories_backup_before_cleanup.json`)
+3. Make your changes
+4. If needed, you can re-import the backup
+
+### 2. Default Categories
+
+The application comes with a set of default categories loaded from `default_categories.json`:
+- **Amazon** categories (Digital, Marketplace, POS)
+- **Apple services** and subscriptions
+- **Streaming services** (Netflix, Peacock, Prime Video)
+- **Gas stations** and transportation
+- **Food delivery** (DoorDash, etc.)
+- **Banking** (Capital One, Cash App)
+- **Entertainment** (Audible, Kindle)
+
+These defaults are automatically loaded when the database is first initialized. You can:
+- **Customize** the `default_categories.json` file to match your preferences
+- **Export** your current categories to see the format
+- **Import** different default sets as needed
+
+### 3. Share Categories with Team/Family
+
+If multiple people use the Transaction Manager:
+1. One person creates and refines category rules
+2. Export the categories
+3. Share the JSON file with others
+4. Others import the categories to get the same rules
+
+### 4. Create Category Templates
+
+Build category sets for different purposes:
+- `categories_personal.json` - Personal expense categories
+- `categories_business.json` - Business expense categories
+- `categories_tax.json` - Tax-related categories
+
+Switch between them by importing as needed.
+
+### 5. Version Control
+
+Store your category files in Git or another version control system to:
+- Track changes over time
+- Revert to previous versions
+- Document why categories changed
+
+## Import Behavior
+
+### New Categories
+Categories that don't exist in your database will be **added**.
+
+### Duplicate Categories (same name)
+Two options:
+
+**Option 1: Skip duplicates** (default)
+- Existing categories remain unchanged
+- Only new categories are added
+- Duplicate names are reported as warnings
+
+**Option 2: Update existing** (checkbox enabled)
+- Categories with matching names are **updated** with new patterns
+- Useful when importing refined versions of categories
+
+### After Import
+After importing categories, you should:
+1. Click **Recategorize All** to apply the new rules to existing transactions
+2. Review the **📊 Summary** tab to see the updated categorization
+
+## Tips & Best Practices
+
+### 1. Use Descriptive Names
+```json
+✓ "Amazon Marketplace"
+✗ "AMZ"
+```
+
+### 2. Add Descriptions
+Help yourself remember what each category is for:
+```json
+{
+  "name": "Subscription Services",
+  "pattern": "NETFLIX|SPOTIFY|HULU",
+  "pattern_type": "regex",
+  "description": "Monthly streaming and entertainment subscriptions"
+}
+```
+
+### 3. Test Patterns Before Exporting
+1. Create a category in the GUI
+2. Click **Recategorize All** to test it
+3. View results in the Summary tab
+4. Once satisfied, export
+
+### 4. Use Colors Consistently
+Assign meaningful colors:
+- 🔴 Red (#F44336) - Mandatory expenses (utilities, rent)
+- 🟢 Green (#4CAF50) - Income, refunds
+- 🔵 Blue (#2196F3) - Discretionary spending
+- 🟡 Yellow (#FFC107) - Variable expenses (groceries, gas)
+
+### 5. Regular Exports
+Export your categories regularly (monthly/quarterly) as backups.
+
+## Troubleshooting
+
+### "Invalid JSON file" Error
+- Ensure the file is valid JSON (use a JSON validator)
+- Check for missing commas, brackets, or quotes
+- Don't edit the file manually unless you're familiar with JSON
+
+### "Category already exists" Warnings
+- This is normal if importing to a database that already has some categories
+- Enable "Update existing categories" if you want to replace them
+- Or manually delete conflicting categories before importing
+
+### Categories Not Matching After Import
+- Click **Recategorize All** in the Manage Categories tab
+- This applies all category rules to existing transactions
+
+### Import Shows 0 Categories
+- Check that the JSON file has the correct format
+- Ensure it has a "categories" array
+- See the sample file: `categories_sample.json`
+
+## Example Workflows
+
+### Weekly Cleanup Workflow
+```
+1. Review uncategorized transactions in Summary tab
+2. Create new categories for common patterns
+3. Click Recategorize All
+4. Export categories → categories_backup_YYYY-MM-DD.json
+```
+
+### Migration to New Computer
+```
+1. On old computer: Export Categories
+2. Copy JSON file to new computer
+3. On new computer: Install Transaction Manager
+4. Import the categories JSON file
+5. Import your transaction database or CSV files
+6. Click Recategorize All
+```
+
+### Sharing with Family Member
+```
+1. Export your refined categories
+2. Email/share the JSON file
+3. Family member imports the file
+4. Both now use consistent categorization rules
+```
+
+## File Format Compatibility
+
+### Current Version: 1.0
+The current export format is version 1.0. Future versions will remain backward compatible.
+
+### Legacy Format Support
+The importer also supports the legacy format (just an array of categories without metadata):
+```json
+[
+  {
+    "name": "Amazon",
+    "pattern": "AMAZON",
+    "pattern_type": "contains"
+  }
+]
+```
+
+## Related Features
+
+- **CSV Import Settings**: See `IMPORT_SETTINGS_GUIDE.md`
+- **Category Management**: Use the Manage Categories tab for creating/editing categories
+- **Recategorize All**: Applies all category rules to existing transactions
+
+## Summary
+
+✓ **Export** - Backup and share your category rules
+✓ **Import** - Restore or load category sets
+✓ **Cherry-Pick** - Select specific categories to export or import
+✓ **JSON Format** - Human-readable and version-control friendly
+✓ **Flexible** - Skip or update duplicates as needed
+✓ **Safe** - Preview before importing, backup before changes
+
+### Key Features
+- **Select All / Deselect All** buttons for quick selection
+- **Checkbox selection** for both import and export
+- **Pattern preview** showing what each category matches
+- **Validation** ensures at least one category is selected
+- **Counts** show exactly how many categories are being processed
+
+For more help, see the main README.md or the application's help documentation.
+
+