Add CACHE_STATUS UART poll and dashboard live stream.

Combine cached accel and tap in one low-overhead master command for ~16 ms
host polling. The dashboard uses a single live-stream toggle plus per-slave
accel-stream controls; fix live_stream state so polling is not cleared every
slow client refresh.

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

main/CMakeLists.txt

@@ -22,6 +22,7 @@ idf_component_register(
   "cmd/cmd_accel_stream.c"
   "cmd/cmd_tap_notify.c"
   "cmd/cmd_tap_snapshot.c"
+  "cmd/cmd_cache_status.c"
   "cmd/cmd_espnow_unicast_test.c"
   "cmd/cmd_espnow_find_me.c"
   "cmd/cmd_restart.c"