fix(commands_v2): write-lock and debug-log v2_queue_consume_stop_after_if

Per code review on commit 97b5bd79:
- consume_stop_after_if mutates inner state on match (clears the
  marker), so use write().await for semantic consistency with the
  other mutating commands. The inner Mutex made read() work today
  but the intent is mutation.
- Demote the per-call log to debug — this fires on every natural
  track-end and would spam info-level logs during normal listening.

Refs #356.

cc

src-tauri/src/commands_v2/queue.rs

@@ -864,9 +864,9 @@ pub async fn v2_queue_consume_stop_after_if(
     finished_track_id: u64,
     bridge: State<'_, CoreBridgeState>,
 ) -> Result<bool, RuntimeError> {
-    log::info!("[V2] queue_consume_stop_after_if: {}", finished_track_id);
+    log::debug!("[V2] queue_consume_stop_after_if: {}", finished_track_id);
     let bridge = bridge.get().await;
-    Ok(bridge.core().queue().read().await.consume_stop_after_if(finished_track_id))
+    Ok(bridge.core().queue().write().await.consume_stop_after_if(finished_track_id))
 }
 
 /// Remove all queue tracks at indices > `index`. Returns the count