Add LiPo battery monitoring with ESP-NOW cache and dashboard API.

Slaves report pack voltages every 30s; the master caches them for fast
BATTERY_STATUS reads. goTool exposes REST/WebSocket and shows values in
the dashboard, with a nanopb fix so optional lipo submessages encode.

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

main/cmd/cmd_handler.c

@@ -52,6 +52,8 @@ static const char *message_type_name(uint16_t id) {
     return "ACCEL_SNAPSHOT";
   case alox_MessageType_ACCEL_STREAM:
     return "ACCEL_STREAM";
+  case alox_MessageType_BATTERY_STATUS:
+    return "BATTERY_STATUS";
   default:
     return "UNKNOWN";
   }