feat: add auth, real-time collaboration, sharing, font control, and UI fixes

Phase 1 - Bug fixes:
- Fix color labels not showing on active line in format preview
- Replace eye emoji with SVG icon showing clear preview/raw state
- Replace // button with comment icon + better tooltip
- Fix ThemePicker accent colors when using system theme

Phase 2 - Font:
- Load JetBrains Mono via Google Fonts with offline fallback
- Add font size control (A-/A+) with keyboard shortcuts
- Persist font size preference in localStorage

Phase 3 - Auth:
- Supabase-based email/password authentication
- Device session management with configurable password renewal TTL
- AuthModal, UserMenu, SecuritySettings components

Phase 4 - Cloud sync:
- Document metadata sync to Supabase PostgreSQL
- Legacy localStorage migration on first login
- IndexedDB persistence via y-indexeddb

Phase 5 - Real-time collaboration:
- Y.js CRDT integration with CodeMirror 6
- Hocuspocus WebSocket server with JWT auth
- Collaborative cursor awareness
- CollabIndicator component

Phase 6 - Sharing:
- Share links with view/edit permissions
- ShareDialog component with copy-to-clipboard
- Minimal client-side router for /s/{token} URLs

Infrastructure:
- Docker Compose with PostgreSQL, GoTrue, PostgREST, Hocuspocus
- Nginx reverse proxy for all backend services
- SQL migrations with RLS policies
- Production-ready Dockerfile with build args

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

calcpad-web/vite.config.ts

@@ -55,6 +55,17 @@ export default defineConfig({
               networkTimeoutSeconds: 5,
             },
           },
+          {
+            urlPattern: /^https:\/\/fonts\.(?:googleapis|gstatic)\.com/,
+            handler: 'CacheFirst',
+            options: {
+              cacheName: 'google-fonts',
+              expiration: {
+                maxEntries: 10,
+                maxAgeSeconds: 60 * 60 * 24 * 365,
+              },
+            },
+          },
           {
             urlPattern: /\.(?:png|jpg|jpeg|svg|gif|webp)$/,
             handler: 'CacheFirst',