fix(mobile): auto-dismiss queue status banner when queue is empty

- Skip flush call and clear lastFlushed when getNoteQueueSize() is 0
- Prevents stale 'Flushed on last attempt: N' persisting after queue drains

mobile/src/app/_layout.tsx

@@ -58,6 +58,12 @@ export default function RootLayout() {
   }
 
   async function flushQueuedNoteMutations(): Promise<void> {
+    const pending = getNoteQueueSize();
+    if (pending === 0) {
+      setQueueStatus({ pending: 0, lastFlushed: 0 });
+      return;
+    }
+
     const result = await flushNoteQueue().catch(() => ({ flushed: 0, failed: getNoteQueueSize() }));
     setQueueStatus({
       pending: result.failed,