Added ECHO cmd and fixed some timing issues

main/proto/uart_messages.proto

@@ -29,6 +29,8 @@ enum MessageType {
   reserved 28;
   /** Combined cached accel + tap poll (one UART round-trip, ~16 ms cadence). */
   CACHE_STATUS = 29;
+  /** Host → master → slave → master: timestamp echo round-trip (latency test). */
+  ESPNOW_ECHO_PING = 30;
 }
 
 message UartMessage {
@@ -63,6 +65,8 @@ message UartMessage {
     TapNotifyResponse tap_notify_response = 30;
     CacheStatusRequest cache_status_request = 33;
     CacheStatusResponse cache_status_response = 34;
+    EspNowEchoPingRequest espnow_echo_ping_request = 35;
+    EspNowEchoPingResponse espnow_echo_ping_response = 36;
   }
 }
 
@@ -255,6 +259,22 @@ message EspNowUnicastTestResponse {
   uint32 seq = 2;
 }
 
+/** Host → master: ESP-NOW echo ping to one slave (timestamp echoed back). */
+message EspNowEchoPingRequest {
+  uint32 client_id = 1;
+  /** Microseconds since Unix epoch (host clock). */
+  uint64 timestamp_us = 2;
+}
+
+message EspNowEchoPingResponse {
+  bool success = 1;
+  uint32 client_id = 2;
+  /** Echoed host timestamp from goTool request. */
+  uint64 timestamp_us = 3;
+  /** esp_timer_get_time() delta from ping send to pong recv (master→slave→master). */
+  uint32 esp_rtt_us = 4;
+}
+
 // Host → master: LED ring on master (client_id=0) and/or slaves via ESP-NOW.
 // mode: 0=clear, 1=progress (0–100 %), 2=digit (0–10), 3=blink, 4=find-me, 5=all LEDs solid color.
 message LedRingProgressRequest {