fix(ui): pin router-plugin version and commit deterministic route tree (#635)

TanStack router-plugin <1.168.21 sorted routes by coercing route nodes
to strings, so output order followed filesystem-walk order and flipped
depending on which generator version a contributor's node_modules
resolved. Pin the version so it cannot drift, commit the sorted output
from the fixed generator, and fail CI if a build produces a different
route tree than the one committed.

.github/workflows/ui.yml

@@ -57,3 +57,6 @@ jobs:
 
       - name: Build Frontend
         run: pnpm build
+
+      - name: Check for generated route tree drift
+        run: git diff --exit-code -- src/routeTree.gen.ts