add usb serial for debug firmware

Code by gpt5.5-xhigh

src/bt.cpp

@@ -298,7 +298,9 @@ static void hci_packet_handler(uint8_t packet_type, uint16_t channel, uint8_t *p
         }
 
         case HCI_EVENT_DISCONNECTION_COMPLETE: {
+#ifndef ENABLE_SERIAL
             tud_disconnect();
+#endif
             gap_connectable_control(1);
             gap_discoverable_control(1);
             const uint8_t reason = hci_event_disconnection_complete_get_reason(packet);
@@ -345,7 +347,9 @@ static void l2cap_packet_handler(uint8_t packet_type, uint16_t channel, uint8_t
                 }else if (size > 1){
                     is_dse = true;
                 }
+#ifndef ENABLE_SERIAL
                 tud_connect();
+#endif
             }
             if (packet[0] == 0xA3) {
                 uint8_t report_id = packet[1];