Fix review findings and remove Uncategorized from sidebar

Backend: cache Google access tokens (drop dead access_token_expires_at,
migration 0007), handle MeTube cleared/canceled events by URL, return
email from /auth/status only when authenticated, move Google base URLs
into settings, run container as non-root.

Frontend: include local feed filters in the query key, remove dead
Saved page and unused assets, drop stale CategoryNav props and classes,
send Content-Type only with a body, remove Uncategorized from sidebar.

backend/app/api/auth.py

@@ -17,11 +17,16 @@ router = APIRouter()
 
 @router.get("/auth/status")
 def auth_status(request: Request, db: Session = Depends(get_db)) -> dict:
+    # This endpoint is public (the Connect page needs `authenticated` before
+    # logging in), so the connected account's email must only be revealed to a
+    # request holding a valid session.
+    authenticated = bool(request.session.get("authenticated"))
     connected = google_oauth.is_connected(db)
+    email = google_oauth.get_connected_email(db) if authenticated and connected else None
     return {
-        "authenticated": bool(request.session.get("authenticated")),
+        "authenticated": authenticated,
         "connected": connected,
-        "email": google_oauth.get_connected_email(db) if connected else None,
+        "email": email,
     }