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/proto/uart_messages.proto

@@ -9,6 +9,7 @@ enum MessageType {
   VERSION = 3;
   CLIENT_INFO = 4;
   CLIENT_INPUT = 5;
+  ACCEL_DEADZONE = 6;
   OTA_START = 16;
   OTA_PAYLOAD = 17;
   OTA_END = 18;
@@ -28,6 +29,8 @@ message UartMessage {
     OtaPayload ota_payload = 8;
     OtaEndPayload ota_end = 9;
     OtaStatusPayload ota_status = 10;
+    AccelDeadzoneRequest accel_deadzone_request = 11;
+    AccelDeadzoneResponse accel_deadzone_response = 12;
   }
 }
 
@@ -67,6 +70,23 @@ message ClientInputResponse {
   repeated ClientInput clients = 1; 
 }
 
+// write=false: read deadzone; write=true: apply deadzone (LSB per axis, raw accel units).
+// client_id 0 = local BMA456 on this node; >0 = slave id on master; ignored on slave.
+// all_clients = true (master only): push deadzone to every registered slave via ESP-NOW.
+message AccelDeadzoneRequest {
+  bool write = 1;
+  uint32 deadzone = 2;
+  uint32 client_id = 3;
+  bool all_clients = 4;
+}
+
+message AccelDeadzoneResponse {
+  uint32 deadzone = 1;
+  uint32 client_id = 2;
+  bool success = 3;
+  uint32 slaves_updated = 4;
+}
+
 message OtaStartPayload {
   uint32 total_size = 1;
   uint32 block_size = 2;