refactor(app): replace providers-snapshot invalidate with refetchIfStale

invalidate() flagged the query stale and kicked off a refetch unconditionally,
causing a loading flash every time the model selector opened. Expose
refetchIfStale() instead so callers only refetch when data is actually stale.

packages/app/src/components/agent-status-bar.tsx

@@ -867,8 +867,7 @@ export const AgentStatusBar = memo(function AgentStatusBar({
   const {
     entries: snapshotEntries,
     isLoading: snapshotIsLoading,
-    isFetching: snapshotIsFetching,
-    invalidate: invalidateSnapshot,
+    refetchIfStale: refetchSnapshotIfStale,
   } = useProvidersSnapshot(serverId, agent?.cwd);
 
   const snapshotModels = useMemo(() => {
@@ -1034,8 +1033,8 @@ export const AgentStatusBar = memo(function AgentStatusBar({
           console.warn("[AgentStatusBar] setAgentFeature failed", error);
         });
       }}
-      isModelLoading={snapshotIsLoading || snapshotIsFetching}
-      onModelSelectorOpen={invalidateSnapshot}
+      isModelLoading={snapshotIsLoading}
+      onModelSelectorOpen={refetchSnapshotIfStale}
       onDropdownClose={onDropdownClose}
       disabled={!client}
     />