Add support for fusing/unfusing JellyLMS zones into synchronized

multi-room groups, addressed by MAC (derived from the `lms-{mac}` device id).

src-tauri/src/commands/playback_mode.rs

@@ -51,6 +51,22 @@ pub async fn playback_mode_transfer_to_remote(
     manager.0.transfer_to_remote(session_id, position).await
 }
 
+/// Set the transferring flag on the playback mode manager.
+///
+/// Used by the frontend remote->local flow to mark the whole two-step sequence
+/// as a transfer, so `player_play_tracks` starts LOCAL playback instead of
+/// casting back to the remote session it's leaving. Always pair `true` with a
+/// later `false` (including on error) so the flag can't stick.
+#[tauri::command]
+#[specta::specta]
+pub async fn playback_mode_set_transferring(
+    manager: State<'_, PlaybackModeManagerWrapper>,
+    transferring: bool,
+) -> Result<(), String> {
+    manager.0.set_transferring(transferring);
+    Ok(())
+}
+
 /// Transfer playback from remote session back to local device
 ///
 /// Parameters: