Add BLE host transport selectable via DIP8 alongside UART.

Master can speak the same framed protobuf protocol over NimBLE or UART; goTool gains -ble, ble-rtt, and ble-stream timing checks for ESP-NOW coexistence.

Co-authored-by: Cursor <cursoragent@cursor.com>

main/app_config.h

@@ -9,6 +9,8 @@
 typedef struct {
   bool master;
   uint8_t network;
+  /** false = UART host, true = BLE host (DIP8; mutual exclusive, boot-only). */
+  bool host_ble;
   char running_partition[APP_RUNNING_PARTITION_LABEL_MAX];
 } app_config_t;