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/const.py

@@ -37,6 +37,9 @@ API_WEBSOCKET = "/api/media/ws"
 API_BROWSER_FOLDERS = "/api/browser/folders"
 API_BROWSER_BROWSE = "/api/browser/browse"
 API_BROWSER_PLAY = "/api/browser/play"
+API_DISPLAY_MONITORS = "/api/display/monitors"
+API_DISPLAY_BRIGHTNESS = "/api/display/brightness"
+API_DISPLAY_POWER = "/api/display/power"
 
 # Service names
 SERVICE_EXECUTE_SCRIPT = "execute_script"