Fix blank UI from root-mounted Gradio SSR

Disable Gradio 5.49.1 SSR for the root-mounted FastAPI app and add a regression test that verifies a frontend asset referenced by the root page is served successfully.

app.py

@@ -195,7 +195,10 @@ def oauth_login():
     return response
 
 
-app = gr.mount_gradio_app(app, demo, path="/")
+# Gradio 5.49.1's Spaces SSR proxy corrupts frontend asset URLs when a Blocks
+# app is mounted at the root path. OAuth still needs the explicit FastAPI mount,
+# so disable SSR here until the upstream root-mount routing bug is fixed.
+app = gr.mount_gradio_app(app, demo, path="/", ssr_mode=False)
 
 
 if __name__ == "__main__":

test_app.py

@@ -1,5 +1,6 @@
 import importlib
 import os
+import re
 from types import SimpleNamespace
 
 from fastapi.testclient import TestClient
@@ -40,3 +41,18 @@ def test_auth_control_uses_top_level_navigation():
     assert 'href="/logout?_target_url=/"' in logged_in
     assert "<script>" not in logged_in
     assert "&lt;script&gt;" in logged_in
+
+
+def test_root_frontend_asset_is_served():
+    """Catch broken asset paths when mounting Gradio at the Space root."""
+    with TestClient(certificate_app.app) as client:
+        response = client.get("/")
+        assert response.status_code == 200
+
+        assets = re.findall(r'(?:src|href)="(\.?/assets/[^"]+)"', response.text)
+        assert assets, "root page did not reference a Gradio frontend asset"
+
+        asset_path = assets[0].removeprefix(".")
+        asset_response = client.get(asset_path)
+
+    assert asset_response.status_code == 200