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/media_player.py

@@ -285,6 +285,8 @@ class RemoteMediaPlayerEntity(CoordinatorEntity[MediaPlayerCoordinator], MediaPl
             | MediaPlayerEntityFeature.PREVIOUS_TRACK
             | MediaPlayerEntityFeature.NEXT_TRACK
             | MediaPlayerEntityFeature.SEEK
+            | MediaPlayerEntityFeature.TURN_ON
+            | MediaPlayerEntityFeature.TURN_OFF
         )
 
     @property
@@ -450,3 +452,24 @@ class RemoteMediaPlayerEntity(CoordinatorEntity[MediaPlayerCoordinator], MediaPl
             await self.coordinator.async_request_refresh()
         except MediaServerError as err:
             _LOGGER.error("Failed to seek: %s", err)
+
+    async def async_turn_on(self) -> None:
+        """Send turn on command."""
+        try:
+            await self.coordinator.client.turn_on()
+        except MediaServerError as err:
+            _LOGGER.error("Failed to turn on: %s", err)
+
+    async def async_turn_off(self) -> None:
+        """Send turn off command."""
+        try:
+            await self.coordinator.client.turn_off()
+        except MediaServerError as err:
+            _LOGGER.error("Failed to turn off: %s", err)
+
+    async def async_toggle(self) -> None:
+        """Send toggle command."""
+        try:
+            await self.coordinator.client.toggle()
+        except MediaServerError as err:
+            _LOGGER.error("Failed to toggle: %s", err)