Add display monitor brightness and power control entities

- Add NUMBER platform for monitor brightness (0-100)
- Add SWITCH platform for monitor power on/off
- Add display API client methods (get_display_monitors, set_display_brightness, set_display_power)
- Add display API constants

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

custom_components/remote_media_player/api_client.py

@@ -30,6 +30,9 @@ from .const import (
     API_BROWSER_FOLDERS,
     API_BROWSER_BROWSE,
     API_BROWSER_PLAY,
+    API_DISPLAY_MONITORS,
+    API_DISPLAY_BRIGHTNESS,
+    API_DISPLAY_POWER,
 )
 
 _LOGGER = logging.getLogger(__name__)
@@ -342,6 +345,42 @@ class MediaServerClient:
         """
         return await self._request("POST", API_BROWSER_PLAY, {"path": file_path})
 
+    async def get_display_monitors(self) -> list[dict[str, Any]]:
+        """Get list of connected monitors with brightness and power info.
+
+        Returns:
+            List of monitor dicts with id, name, brightness, power_supported, power_on, resolution
+        """
+        return await self._request("GET", f"{API_DISPLAY_MONITORS}?refresh=true")
+
+    async def set_display_brightness(self, monitor_id: int, brightness: int) -> dict[str, Any]:
+        """Set brightness for a specific monitor.
+
+        Args:
+            monitor_id: Monitor index
+            brightness: Brightness level (0-100)
+
+        Returns:
+            Response data with success status
+        """
+        return await self._request(
+            "POST", f"{API_DISPLAY_BRIGHTNESS}/{monitor_id}", {"brightness": brightness}
+        )
+
+    async def set_display_power(self, monitor_id: int, on: bool) -> dict[str, Any]:
+        """Set power state for a specific monitor.
+
+        Args:
+            monitor_id: Monitor index
+            on: True to turn on, False to turn off
+
+        Returns:
+            Response data with success status
+        """
+        return await self._request(
+            "POST", f"{API_DISPLAY_POWER}/{monitor_id}", {"on": on}
+        )
+
 
 class MediaServerWebSocket:
     """WebSocket client for real-time media status updates."""