Add UART ACCEL_READ command for on-demand BMA456 samples.

Expose MessageType 24 with protobuf response (success, x, y, z in raw LSB),
firmware handler with mutex-safe I2C read, goTool `accel` CLI, and docs.

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

goTool/main.go

@@ -16,6 +16,7 @@ func usage() {
 	fmt.Fprintf(os.Stderr, "  version   firmware version and git hash\n")
 	fmt.Fprintf(os.Stderr, "  clients   registered ESP-NOW slaves on the master\n")
 	fmt.Fprintf(os.Stderr, "  deadzone      get/set accelerometer deadzone (LSB)\n")
+	fmt.Fprintf(os.Stderr, "  accel         read current accelerometer XYZ (raw LSB)\n")
 	fmt.Fprintf(os.Stderr, "  unicast-test  send ESP-NOW unicast test to one slave\n")
 	fmt.Fprintf(os.Stderr, "  test          run automated scenario (see testdata/)\n")
 	fmt.Fprintf(os.Stderr, "  serve         web dashboard (Bootstrap + WebSocket)\n")
@@ -50,7 +51,7 @@ func main() {
 			os.Exit(2)
 		}
 		runErr = runServe(*portName, *baud, flag.Args()[1:])
-	case "version", "clients", "client-info", "deadzone", "accel-deadzone", "unicast-test", "unicast_test", "led-ring", "led_ring", "find-me", "find_me", "restart", "ota", "ota-progress", "ota_progress":
+	case "version", "clients", "client-info", "deadzone", "accel-deadzone", "accel", "accel-read", "accel_read", "unicast-test", "unicast_test", "led-ring", "led_ring", "find-me", "find_me", "restart", "ota", "ota-progress", "ota_progress":
 		if *portName == "" {
 			fmt.Fprintf(os.Stderr, "command %q requires -port\n\n", cmd)
 			usage()
@@ -68,6 +69,8 @@ func main() {
 			runErr = runClients(sp)
 		case "deadzone", "accel-deadzone":
 			runErr = runDeadzone(sp, flag.Args()[1:])
+		case "accel", "accel-read", "accel_read":
+			runErr = runAccel(sp)
 		case "unicast-test", "unicast_test":
 			runErr = runUnicastTest(sp, flag.Args()[1:])
 		case "led-ring", "led_ring":