Stream slave accel via ESP-NOW with master snapshot cache.

Slaves push BMA456 samples at 16ms when enabled; the master caches per
client and exposes ACCEL_SNAPSHOT and ACCEL_STREAM over UART. goTool adds
dashboard stream controls, HTTP accel-stream routes, and an external
WebSocket API with per-connection receive/interval and slave stream commands.

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

main/cmd/cmd_accel_stream.h

@@ -0,0 +1,6 @@
+#ifndef CMD_ACCEL_STREAM_H
+#define CMD_ACCEL_STREAM_H
+
+void cmd_accel_stream_register(void);
+
+#endif