docs: add CLAUDE.md for Claude Code guidance

Author: kasvith

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+Op Notes is a surgical notes management desktop application for hospitals built with Electron, React, and SQLite. It manages patient records, surgery notes, doctor information, and follow-up records.
+
+## Common Commands
+
+```bash
+pnpm install          # Install dependencies
+pnpm dev              # Development mode with hot reload
+pnpm build            # Full build with typecheck
+pnpm lint             # ESLint with auto-fix
+pnpm typecheck        # TypeScript compilation check
+pnpm format           # Run prettier formatter
+pnpm build:mac        # Build macOS app
+pnpm build:win        # Build Windows installer
+pnpm build:linux      # Build Linux packages
+```
+
+## Architecture
+
+### Electron Process Structure
+
+```
+Main Process (src/main/)
+├── index.ts          # Window creation, auto-update, IPC setup
+├── api.ts            # Centralized IPC handler routing
+├── db.ts             # Kysely + SQLite initialization
+├── db/migrations/    # Database schema migrations
+└── repository/       # Data access layer (patient.ts, doctor.ts, surgery.ts)
+
+Preload (src/preload/)
+└── index.ts          # Context bridge exposing window.api.invoke()
+
+Renderer Process (src/renderer/src/)
+├── main.tsx          # React root with router, QueryClient, providers
+├── routes/           # Page components (patients/, doctors/, surgeries/, settings/)
+├── components/       # UI components (ui/ for Radix/Shadcn, domain-specific folders)
+├── contexts/         # React Context providers
+├── hooks/            # Custom React hooks
+└── lib/queries.ts    # React Query key factory
+```
+
+### IPC Communication Pattern
+
+All renderer-to-main communication uses a single IPC channel:
+```typescript
+// Renderer calls:
+window.api.invoke('methodName', ...args)
+
+// Main process handles in api.ts:
+ipcMain.handle('invokeApiCall', (event, method, ...args) => api[method](...args))
+```
+
+API methods return `{ result }` on success or `{ error }` on failure.
+
+### Database
+
+- **Engine**: SQLite with better-sqlite3, Kysely query builder
+- **Location**: `~/.opnotes/data.db`
+- **Tables**: patients, doctors, surgeries, surgery_followups, surgery_doctors_done_by, surgery_doctors_assisted_by, app_settings
+- **FTS tables**: patients_fts, surgeries_fts, doctors_fts for full-text search
+- **Migrations**: Code-based in `src/main/db/migrations/`
+
+### Key Type Definitions
+
+- Database schema types: `src/shared/types/db.d.ts`
+- API filter types: `src/shared/types/api.d.ts`
+- Preload API types: `src/preload/index.d.ts`
+
+### State Management
+
+- **Server state**: React Query with 10-second stale time
+- **Forms**: React Hook Form with Zod validation
+- **Global settings**: React Context (SettingsContext)
+- **Routing**: React Router with hash-based routing
+
+### Printing
+
+Separate print window loads `src/renderer/print.html`. Data passed via IPC `printData` event. Templates use Handlebars in `resources/templates/`.
+
+## Tech Stack
+
+- Electron 28 + electron-vite
+- React 18 + TypeScript 5.3
+- Kysely (type-safe SQL) + better-sqlite3
+- Tailwind CSS + Radix UI + Shadcn components
+- TipTap for rich text editing
+- React Query for data fetching