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/CMakeLists.txt

@@ -18,7 +18,8 @@ idf_component_register(
   "cmd/cmd_version.c"
   "cmd/cmd_client_info.c"
   "cmd/cmd_accel_deadzone.c"
-  "cmd/cmd_accel_read.c"
+  "cmd/cmd_accel_snapshot.c"
+  "cmd/cmd_accel_stream.c"
   "cmd/cmd_espnow_unicast_test.c"
   "cmd/cmd_espnow_find_me.c"
   "cmd/cmd_restart.c"