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/package.json

@@ -17,9 +17,15 @@
     "@codemirror/state": "^6.5.2",
     "@codemirror/view": "^6.36.5",
     "@lezer/highlight": "^1.2.1",
+    "@supabase/supabase-js": "^2.99.3",
     "codemirror": "^6.0.1",
+    "nanoid": "^5.1.7",
     "react": "^19.2.4",
-    "react-dom": "^19.2.4"
+    "react-dom": "^19.2.4",
+    "y-codemirror.next": "^0.3.5",
+    "y-indexeddb": "^9.0.12",
+    "y-websocket": "^3.0.0",
+    "yjs": "^13.6.30"
   },
   "devDependencies": {
     "@types/react": "^19.2.14",