Add accelerometer deadzone via UART and ESP-NOW.

Filter BMA456 logs by configurable LSB threshold; master can set deadzone
for local sensor or slaves using ACCEL_DEADZONE (UART) and ESP-NOW broadcast
until unicast delivery is restored.

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

main/client_registry.c

@@ -60,6 +60,7 @@ static client_slot_t *alloc_slot(const uint8_t mac[CLIENT_MAC_LEN],
       slot = &s_clients[i];
       slot->active = true;
       memcpy(slot->info.mac, mac, CLIENT_MAC_LEN);
+      slot->info.accel_deadzone = CLIENT_REGISTRY_DEFAULT_ACCEL_DEADZONE;
       if (out_is_new != NULL) {
         *out_is_new = true;
       }
@@ -169,6 +170,59 @@ size_t client_registry_count(void) {
   return n;
 }
 
+const client_info_t *client_registry_find_by_id(uint32_t id) {
+  for (size_t i = 0; i < CLIENT_REGISTRY_MAX; i++) {
+    if (s_clients[i].active && s_clients[i].info.id == id) {
+      return &s_clients[i].info;
+    }
+  }
+  return NULL;
+}
+
+esp_err_t client_registry_set_accel_deadzone(uint32_t client_id,
+                                             uint32_t deadzone) {
+  const client_info_t *info = client_registry_find_by_id(client_id);
+  if (info == NULL) {
+    return ESP_ERR_NOT_FOUND;
+  }
+
+  for (size_t i = 0; i < CLIENT_REGISTRY_MAX; i++) {
+    if (s_clients[i].active && s_clients[i].info.id == client_id) {
+      s_clients[i].info.accel_deadzone = deadzone;
+      return ESP_OK;
+    }
+  }
+  return ESP_ERR_NOT_FOUND;
+}
+
+esp_err_t client_registry_get_accel_deadzone(uint32_t client_id,
+                                             uint32_t *deadzone_out) {
+  if (deadzone_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;
+  }
+
+  *deadzone_out = info->accel_deadzone;
+  return ESP_OK;
+}
+
+size_t client_registry_set_accel_deadzone_all(uint32_t deadzone) {
+  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_deadzone = deadzone;
+    n++;
+  }
+  return n;
+}
+
 const client_info_t *client_registry_at(size_t index) {
   size_t n = 0;
   for (size_t i = 0; i < CLIENT_REGISTRY_MAX; i++) {