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/client_registry.c

@@ -241,6 +241,85 @@ size_t client_registry_set_accel_deadzone_all(uint32_t deadzone) {
   return n;
 }
 
+static void clear_client_accel(client_slot_t *slot) {
+  if (slot == NULL) {
+    return;
+  }
+  slot->info.accel_valid = false;
+  slot->info.accel_x = 0;
+  slot->info.accel_y = 0;
+  slot->info.accel_z = 0;
+  slot->info.accel_updated_at = 0;
+}
+
+esp_err_t client_registry_set_accel_stream(uint32_t client_id, bool enabled) {
+  for (size_t i = 0; i < CLIENT_REGISTRY_MAX; i++) {
+    if (!s_clients[i].active || s_clients[i].info.id != client_id) {
+      continue;
+    }
+    s_clients[i].info.accel_stream_enabled = enabled;
+    if (!enabled) {
+      clear_client_accel(&s_clients[i]);
+    }
+    return ESP_OK;
+  }
+  return ESP_ERR_NOT_FOUND;
+}
+
+esp_err_t client_registry_get_accel_stream(uint32_t client_id,
+                                           bool *enabled_out) {
+  if (enabled_out == NULL) {
+    return ESP_ERR_INVALID_ARG;
+  }
+  const client_info_t *info = client_registry_find_by_id(client_id);
+  if (info == NULL) {
+    return ESP_ERR_NOT_FOUND;
+  }
+  *enabled_out = info->accel_stream_enabled;
+  return ESP_OK;
+}
+
+size_t client_registry_set_accel_stream_all(bool enabled) {
+  size_t n = 0;
+  for (size_t i = 0; i < CLIENT_REGISTRY_MAX; i++) {
+    if (!s_clients[i].active) {
+      continue;
+    }
+    s_clients[i].info.accel_stream_enabled = enabled;
+    if (!enabled) {
+      clear_client_accel(&s_clients[i]);
+    }
+    n++;
+  }
+  return n;
+}
+
+esp_err_t client_registry_update_accel(const uint8_t mac[CLIENT_MAC_LEN],
+                                       uint32_t slave_id, int16_t x, int16_t y,
+                                       int16_t z) {
+  if (mac == NULL) {
+    return ESP_ERR_INVALID_ARG;
+  }
+
+  client_slot_t *slot = find_slot(mac);
+  if (slot == NULL) {
+    return ESP_ERR_NOT_FOUND;
+  }
+  if (slot->info.id != slave_id) {
+    return ESP_ERR_INVALID_ARG;
+  }
+  if (!slot->info.accel_stream_enabled) {
+    return ESP_ERR_INVALID_STATE;
+  }
+
+  slot->info.accel_x = x;
+  slot->info.accel_y = y;
+  slot->info.accel_z = z;
+  slot->info.accel_valid = true;
+  slot->info.accel_updated_at = now_ms();
+  return ESP_OK;
+}
+
 const client_info_t *client_registry_at(size_t index) {
   size_t n = 0;
   for (size_t i = 0; i < CLIENT_REGISTRY_MAX; i++) {