fix: correct MIDI channel processing and port cleanup

Co-authored-by: aider (deepseek/deepseek-reasoner) <aider@aider.chat>

src/midi.c

@@ -66,6 +66,10 @@ void midi_handle_events(void *port_buffer, jack_nframes_t nframes) {
               command_t cmd = {.type = CMD_STOP, .channel = -1, .data = 0};
               queue_push(&cmd_queue, cmd);
             } break;
+            case 66: {
+              command_t cmd = {.type = CMD_ADD_MIDI_CHANNEL, .channel = -1, .data = 0};
+              queue_push(&cmd_queue_main_midi, cmd);
+            } break;
             default:
               break;
             }