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/client/create/Create.tsx

@@ -7,9 +7,12 @@ import {
   PageHero,
   PageHeroSection,
 } from '../../../components/page';
-import { CreateSpaceForm } from '../../../features/create-space';
 import { useRoomNavigate } from '../../../hooks/useRoomNavigate';
 
+const CreateSpaceForm = React.lazy(() =>
+  import('../../../features/create-space').then((m) => ({ default: m.CreateSpaceForm })),
+);
+
 export function Create() {
   const { navigateSpace } = useRoomNavigate();
 
@@ -26,7 +29,9 @@ export function Create() {
                     title="Create Space"
                     subTitle="Build a space for your community."
                   />
-                  <CreateSpaceForm onCreate={navigateSpace} />
+                  <React.Suspense fallback={null}>
+                    <CreateSpaceForm onCreate={navigateSpace} />
+                  </React.Suspense>
                 </Box>
               </PageHeroSection>
             </PageContentCenter>