feat: add frontend README and backend test database

- Create frontend/README.md with setup, testing, and API integration instructions
- Add backend test database file for local testing
- Implement README validation tests to ensure documentation completeness
- Update project documentation to reflect new structure and features

frontend/README.md

@@ -0,0 +1,49 @@
+# Frontend - Quasar Game Library
+
+React + Vite + React Query UI for Quasar.
+
+## Setup
+
+```bash
+cd frontend
+yarn install
+yarn dev  # Start Vite dev server on http://localhost:5173
+```
+
+## Testing
+
+```bash
+yarn test       # Run Vitest in watch mode
+yarn test:run   # Run once
+```
+
+## Building
+
+```bash
+yarn build      # Build for production (dist/)
+yarn preview    # Preview production build locally
+```
+
+## Structure
+
+```
+src/
+├── routes/          # Page components
+├── components/      # Reusable components
+├── hooks/           # TanStack Query hooks
+├── lib/             # API client, utilities
+├── types/           # TypeScript types
+└── styles.css       # Tailwind CSS
+```
+
+## API Integration
+
+Backend API runs on `http://localhost:3000`.
+
+Frontend proxies requests via `.env`:
+
+```
+VITE_API_URL=http://localhost:3000
+```
+
+All API calls go through `src/lib/api.ts`.