fix(codex): align fallback metadata and remove stale models automatically

- Align fallback defaults and instruction structure with upstream Codex while preserving Fast availability for all models
- Stop forcing fallback reasoning levels or inferring original-image support
- Sync managed catalogs on model refresh, configuration changes, and every 30 seconds
- Remove unavailable models, replace missing defaults, and handle empty-list recovery
- Preserve existing configuration on request failures or invalid responses
- Serialize refreshes, update UI model lists, and preserve backups across restarts
- Add regression coverage for fallback compatibility, stale-model cleanup, and configuration recovery

src/pages/AgentsPage.tsx

@@ -783,6 +783,7 @@ export function AgentsPage({ embedded = false, onConfigurationApplied }: AgentsP
       void loadStatuses().catch((requestError) => {
         if (!disposed) setDetectionError(String(requestError));
       });
+      void loadModels(selected);
     }).then((unlisten) => {
       if (disposed) unlisten();
       else stop = unlisten;
@@ -791,7 +792,7 @@ export function AgentsPage({ embedded = false, onConfigurationApplied }: AgentsP
       disposed = true;
       stop?.();
     };
-  }, [loadStatuses]);
+  }, [loadModels, loadStatuses, selected]);
 
   useEffect(() => {
     writeSelectedAgentClient(selected);