Add client registry and CLIENT_INFO UART command on master.

Track ESP-NOW slaves in a shared registry and respond to CLIENT_INFO
with protobuf ClientInfoResponse; ESP-NOW path upserts registry entries.

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

main/powerpod.c

@@ -1,5 +1,6 @@
 #include "app_config.h"
 #include "cmd_handler.h"
+#include "cmd_client_info.h"
 #include "cmd_version.h"
 #include "esp_now_comm.h"
 #include "powerpod.h"
@@ -133,6 +134,7 @@ void app_main(void) {
     init_cmdHandler(cmd_queue);
     init_uart(cmd_queue);
     cmd_version_register();
+    cmd_client_info_register();
   }
 
   uint8_t current_digit = 10;