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/README.md

@@ -73,6 +73,7 @@ Schema: `proto/esp_now_messages.proto`. Encode/decode: `esp_now_proto.c`. The ES
 | `ESPNOW_DISCOVER` | Master → broadcast `FF:FF:FF:FF:FF:FF` | `EspNowDiscover` (`network`) |
 | `ESPNOW_SLAVE_INFO` | Slave → master | `EspNowSlavePresence` |
 | `ESPNOW_HEARTBEAT` | Slave → master | `EspNowSlavePresence` (same fields) |
+| `ESPNOW_SET_ACCEL_DEADZONE` | Master → slave | `EspNowAccelDeadzone` (`deadzone` LSB) |
 
 `EspNowSlavePresence`: `network`, `mac` (6 bytes), `version`, `slave_id`, `available`, `used`.
 
@@ -146,6 +147,7 @@ Host and master speak nanopb-encoded `UartMessage` inside UART frames (byte 0 =
 | 3 | `VERSION` | Implemented (`cmd_version.c`) |
 | 4 | `CLIENT_INFO` | Implemented (`cmd_client_info.c`) — slave list from registry |
 | 5 | `CLIENT_INPUT` | Planned |
+| 6 | `ACCEL_DEADZONE` | Implemented (`cmd_accel_deadzone.c`) — get/set accel filter LSB |
 | 16–20 | OTA / ESP-NOW OTA | Planned |
 
 Regenerate C code:
@@ -173,6 +175,21 @@ Build embeds `POWERPOD_GIT_HASH` via `git rev-parse` in `main/CMakeLists.txt`.
 
 Encoding: `uart_send_uart_message()` in `uart_proto.c`.
 
+### ACCEL_DEADZONE command
+
+Filters BMA456 logs: a new accel line is emitted only when any axis changes by more than `deadzone` raw LSB since the last reported sample (default **100**).
+
+**Request:** framed `06` + nanopb `UartMessage` with `accel_deadzone_request`:
+
+| Field | Meaning |
+|-------|---------|
+| `write` | `false` = read, `true` = write |
+| `deadzone` | Threshold in LSB (write) |
+| `client_id` | `0` = local sensor on this node; `>0` = slave id (master) |
+| `all_clients` | Master: ESP-NOW push to every registered slave |
+
+**Response:** `accel_deadzone_response` with applied `deadzone`, `success`, and `slaves_updated` (ESP-NOW count).
+
 ### CLIENT_INFO command
 
 **Request:** framed payload `04` only (`MessageType.CLIENT_INFO`).