Add comprehensive PWA configuration to make Grimoire installable as a standalone app:
- Install and configure vite-plugin-pwa for automated PWA setup
- Create grimoire-themed app icon (purple book with magical rune)
- Configure web app manifest with app metadata, theme colors, and shortcuts
- Add service worker with Workbox for offline capabilities and font caching
- Add PWA meta tags to index.html for iOS and Android compatibility
- Enable auto-update for service worker registration
The app is now installable on mobile devices and desktop browsers.
