Stream slave accel via ESP-NOW with master snapshot cache.

Slaves push BMA456 samples at 16ms when enabled; the master caches per
client and exposes ACCEL_SNAPSHOT and ACCEL_STREAM over UART. goTool adds
dashboard stream controls, HTTP accel-stream routes, and an external
WebSocket API with per-connection receive/interval and slave stream commands.

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

main/esp_now_comm.h

@@ -7,6 +7,10 @@
 
 esp_err_t esp_now_comm_init(const app_config_t *config);
 
+/** Master: enable/disable accel ESP-NOW stream on one slave. */
+esp_err_t esp_now_comm_send_accel_stream(const uint8_t mac[CLIENT_MAC_LEN],
+                                         uint32_t client_id, bool enable);
+
 /** Master: unicast accel deadzone to one slave (client_id is echoed for filtering). */
 esp_err_t esp_now_comm_send_accel_deadzone(const uint8_t mac[CLIENT_MAC_LEN],
                                            uint32_t client_id, uint32_t deadzone);