fix: code splitting, route errors, Sentry CI source maps

- Lazy-import CreateRoomForm/CreateSpaceForm in CreateRoom.tsx and Create.tsx
  so create-room and create-space get their own chunks; eliminates
  INEFFECTIVE_DYNAMIC_IMPORT warnings
- Add RouteError component wired to root route errorElement so crashes show
  a reload button instead of React Router dev screen
- ci.yml: use secrets.SENTRY_AUTH_TOKEN so source maps upload on CI builds

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -28,7 +28,7 @@ jobs:
         run: npm run build
         env:
           NODE_OPTIONS: '--max_old_space_size=4096'
-          SENTRY_AUTH_TOKEN: ''
+          SENTRY_AUTH_TOKEN: ${{ secrets.SENTRY_AUTH_TOKEN }}
           VITE_APP_VERSION: ${{ github.sha }}
 
       # ── Quality checks (informational — pre-existing issues exist) ───────