Add turn_on/turn_off/toggle support

- Add API_TURN_ON, API_TURN_OFF, API_TOGGLE constants
- Add turn_on(), turn_off(), toggle() methods to MediaServerClient
- Implement async_turn_on, async_turn_off, async_toggle in media player
- Add TURN_ON and TURN_OFF to supported features
- Update README with turn on/off/toggle documentation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

custom_components/remote_media_player/const.py

@@ -28,6 +28,9 @@ API_PREVIOUS = "/api/media/previous"
 API_VOLUME = "/api/media/volume"
 API_MUTE = "/api/media/mute"
 API_SEEK = "/api/media/seek"
+API_TURN_ON = "/api/media/turn_on"
+API_TURN_OFF = "/api/media/turn_off"
+API_TOGGLE = "/api/media/toggle"
 API_SCRIPTS_LIST = "/api/scripts/list"
 API_SCRIPTS_EXECUTE = "/api/scripts/execute"
 API_WEBSOCKET = "/api/media/ws"