Fix ESP-NOW unicast by using sender MAC in client registry.

Register slaves from recv src_addr instead of protobuf mac bytes, add
ESPNOW_UNICAST_TEST for path verification, restore unicast deadzone, and
expose unicast-test in goTool.

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

main/powerpod.c

@@ -1,6 +1,7 @@
 #include "app_config.h"
 #include "cmd_handler.h"
 #include "cmd_accel_deadzone.h"
+#include "cmd_espnow_unicast_test.h"
 #include "cmd_client_info.h"
 #include "cmd_version.h"
 #include "esp_now_comm.h"
@@ -146,6 +147,7 @@ void app_main(void) {
     cmd_version_register();
     cmd_client_info_register();
     cmd_accel_deadzone_register();
+    cmd_espnow_unicast_test_register();
   }
 
   uint8_t current_digit = 10;