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/CMakeLists.txt

@@ -16,6 +16,7 @@ idf_component_register(
   "cmd_handler.c"
   "cmd_version.c"
   "cmd_client_info.c"
+  "cmd_accel_deadzone.c"
   "client_registry.c"
   "esp_now_comm.c"
   "esp_now_proto.c"