feat: PWA support — installable app, Web Push notifications, app badge
Phase 1: Installable PWA
- Add web app manifest with multi-size icons (192, 512, maskable, apple-touch)
- Add PWA meta tags to all entry points (shell.ts, canvas.html, index.html, create-space.html)
- Register service worker on all pages (previously only canvas.html)
- Add manifest.json to precache core list
- Capture beforeinstallprompt for custom install UX
Phase 2: Web Push Notifications
- Add web-push dependency + push_subscriptions DB table
- VAPID key endpoint, subscribe/unsubscribe routes in notification-routes.ts
- Web Push delivery in notify() with auto-cleanup of expired subscriptions
- SW push + notificationclick event handlers
- Client push subscription flow in notification bell component
Phase 3: Install UX Polish
- App badge (setAppBadge/clearAppBadge) on unread count changes
- "Enable push" button in notification panel header
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>