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>

src/app/pages/Router.tsx

@@ -63,6 +63,7 @@ import { UserRoomProfileRenderer } from '../components/UserRoomProfileRenderer';
 import { HomeCreateRoom } from './client/home/CreateRoom';
 import { Create } from './client/create';
 import { getFallbackSession } from '../state/sessions';
+import { RouteError } from './RouteError';
 import { CallStatusRenderer } from './CallStatusRenderer';
 import { CallEmbedProvider } from '../components/CallEmbedProvider';
 
@@ -107,7 +108,7 @@ export const createRouter = (clientConfig: ClientConfig, screenSize: ScreenSize)
   const mobile = screenSize === ScreenSize.Mobile;
 
   const routes = createRoutesFromElements(
-    <Route HydrateFallback={() => null}>
+    <Route HydrateFallback={() => null} errorElement={<RouteError />}>
       <Route
         index
         loader={() => {