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>

goTool/cmd_deadzone.go

@@ -0,0 +1,58 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+
+	"google.golang.org/protobuf/proto"
+
+	"powerpod/gotool/pb"
+)
+
+func runDeadzone(sp *serialPort, args []string) error {
+	fs := flag.NewFlagSet("deadzone", flag.ExitOnError)
+	write := fs.Bool("set", false, "write deadzone (default: read)")
+	deadzone := fs.Uint("value", 100, "deadzone in raw accel LSB (with -set)")
+	clientID := fs.Uint("client", 0, "client id (0=local master BMA456)")
+	all := fs.Bool("all", false, "apply to all registered slaves (master only)")
+	if err := fs.Parse(args); err != nil {
+		return err
+	}
+
+	req := &pb.AccelDeadzoneRequest{
+		Write:       *write,
+		Deadzone:    uint32(*deadzone),
+		ClientId:    uint32(*clientID),
+		AllClients:  *all,
+	}
+	msg := &pb.UartMessage{
+		Type: pb.MessageType_ACCEL_DEADZONE,
+		Payload: &pb.UartMessage_AccelDeadzoneRequest{
+			AccelDeadzoneRequest: req,
+		},
+	}
+	body, err := proto.Marshal(msg)
+	if err != nil {
+		return fmt.Errorf("encode request: %w", err)
+	}
+
+	payload := append([]byte{byte(pb.MessageType_ACCEL_DEADZONE)}, body...)
+	respPayload, err := sp.exchangePayload(payload, "ACCEL_DEADZONE")
+	if err != nil {
+		return err
+	}
+
+	var respMsg pb.UartMessage
+	if err := proto.Unmarshal(respPayload[1:], &respMsg); err != nil {
+		return fmt.Errorf("decode response: %w", err)
+	}
+
+	r := respMsg.GetAccelDeadzoneResponse()
+	if r == nil {
+		return fmt.Errorf("response missing accel_deadzone_response")
+	}
+
+	fmt.Printf("deadzone=%d client_id=%d success=%v slaves_updated=%d\n",
+		r.GetDeadzone(), r.GetClientId(), r.GetSuccess(), r.GetSlavesUpdated())
+	return nil
+}