fix: skip CoreBridge actions for echo SET_STATE commands

The server echoes every state report as a SET_STATE with only next_track
(playing_state=null, current_track=null). These echoes were triggering
align_corebridge_queue_cursor which uses the accumulated renderer state
current_track (from a different context, e.g. iOS). When the track
wasn't found in the local queue, it replaced the entire queue with a
single track, destroying the user's loaded queue.

Now echo SET_STATE commands are detected early and only update the
internal renderer state (for next_track tracking). CoreBridge actions
(align cursor, load track, play/pause) and state reports are skipped
entirely for these echoes.

crates/qconnect-app/src/app.rs

@@ -313,16 +313,38 @@ where
             return Ok(());
         };
 
+        // Detect echo SET_STATE commands: the server echoes every state report
+        // as a SET_STATE with only next_track (playing_state=None, current_track=None).
+        // These echoes must NOT trigger CoreBridge actions (align cursor, load track,
+        // resume/pause) or state reports, otherwise they destroy the local queue
+        // and cause feedback loops.
+        let is_echo = matches!(
+            &renderer_command,
+            RendererCommand::SetState {
+                playing_state,
+                current_track,
+                ..
+            } if playing_state.is_none() && current_track.is_none()
+        );
+
         let (snapshot, queue_version) = {
             let mut state = self.state.lock().await;
             apply_renderer_command(&mut state.renderer, &renderer_command, now_ms());
             (state.renderer.clone(), state.queue.version)
         };
 
+        // Always update renderer state (for tracking next_track etc.)
         self.sink
             .on_event(QconnectAppEvent::RendererUpdated(snapshot.clone()))
             .await;
 
+        if is_echo {
+            log::debug!(
+                "[QConnect] Skipping echo SET_STATE (no playing_state or current_track)"
+            );
+            return Ok(());
+        }
+
         self.sink
             .on_event(QconnectAppEvent::RendererCommandApplied {
                 command: renderer_command.clone(),