docs: Add comprehensive local development & screenshot guide

## New Documentation

### LOCAL_DEVELOPMENT.md (30KB)
Complete guide for building and running locally:
- Platform-specific build commands (Android, iOS, Desktop, Web)
- Screenshot capture instructions for all platforms
- Video/GIF recording techniques
- Build times and troubleshooting
- Development tips and tricks

### Screenshot Capture Scripts
New helper scripts in scripts/:
- screenshot-android.sh - ADB screenshot helper
- screenshot-ios.sh - iOS Simulator screenshot helper
- capture-all-screenshots.sh - Interactive workflow for all platforms

### Directory Structure
Created standardized screenshot organization:

## Build Commands Summary

### Quick Start
```bash
# Android
./gradlew :composeApp:assembleDebug

# iOS
open iosApp/iosApp.xcodeproj

# Desktop
./gradlew :composeApp:run

# Web
./gradlew :composeApp:jsBrowserDevelopmentRun --continuous
```

### Screenshot Capture
```bash
# Setup directories
./scripts/capture-all-screenshots.sh

# Android
./scripts/screenshot-android.sh docs/screenshots/android/chat/main.png

# iOS
./scripts/screenshot-ios.sh docs/screenshots/ios/chat/main.png
```

## Features

### Platform Coverage
- ✅ Android (APK build, ADB screenshots)
- ✅ iOS (Xcode build, Simulator screenshots)
- ✅ Desktop (macOS/Linux/Windows build & screenshots)
- ✅ Web (Webpack build, browser screenshots)

### Screenshot Methods
- Command-line scripts (automated)
- GUI tools (manual)
- Headless capture (Playwright for web)
- Video recording & GIF conversion

### Developer Experience
- Fast incremental builds (--configuration-cache)
- Live reload for web
- Clean build instructions
- Troubleshooting section
- Naming conventions

## Benefits

✅ Onboard new developers faster
✅ Consistent documentation workflow
✅ Automated screenshot capture
✅ All platforms covered
✅ Production-ready examples

## Updated Files
A  docs/LOCAL_DEVELOPMENT.md (30KB)
M  docs/README.md (added links)
A  scripts/capture-all-screenshots.sh (executable)
A  scripts/screenshot-android.sh (executable)
A  scripts/screenshot-ios.sh (executable)

Ready for: Developers to build locally and capture screenshots

Author: brentmzey