Add TEST_ENTER/TEST_EXIT commands via BLE to enter/exit test mode. In test mode, inference results are suppressed; testers can directly trigger BLE JSON (TEST_BLE *), CAN+Buzzer actions (TEST_CAN *), or run sequenced full-coverage tests (TEST_BLE_ALL, TEST_CAN_ALL, TEST_ALL). Auto-exits after 60s idle. Routes unrecognised BLE commands through new bt_uart_set_extra_cmd_cb() hook.