Fix iOS zoom and production API configuration

- Fix iOS auto-zoom on input focus (set font-size: 16px)
- Lock viewport to prevent manual zoom (maximum-scale=1.0)
- Make API URL configurable via VITE_API_URL environment variable
- Add TypeScript types for Vite environment variables
- Create deployment guide with Vercel/backend setup instructions
- Add .env.example for local development configuration
- Add vercel.json for unified frontend/backend deployment

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.env.example

@@ -0,0 +1,4 @@
+# API URL for MIDI search/fetch backend
+# Development: http://localhost:3001
+# Production: Your deployed backend URL (e.g., https://your-api.vercel.app)
+VITE_API_URL=http://localhost:3001