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/src/editor/CalcEditor.tsx

@@ -194,7 +194,7 @@ const calcpadHighlight = HighlightStyle.define([
 const calcpadEditorTheme = EditorView.baseTheme({
   '&': {
     height: '100%',
-    fontSize: '15px',
+    fontSize: 'var(--editor-font-size, 15px)',
     fontFamily: 'var(--mono, ui-monospace, Consolas, "Courier New", monospace)',
   },
   '.cm-scroller': {
@@ -218,7 +218,7 @@ const calcpadEditorTheme = EditorView.baseTheme({
     padding: '0 6px 0 12px',
     color: 'var(--text, #9ca3af)',
     opacity: '0.4',
-    fontSize: '13px',
+    fontSize: 'calc(var(--editor-font-size, 15px) - 2px)',
     minWidth: '32px',
   },
   '.cm-activeLineGutter .cm-gutterElement': {