Add WebSocket support for real-time media status updates

Replace HTTP polling with WebSocket push notifications for instant
state change responses. Server broadcasts updates only when significant
changes occur (state, track, volume, etc.) while letting Home Assistant
interpolate position during playback. Includes seek detection for
timeline updates and automatic fallback to HTTP polling if WebSocket
disconnects.

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

custom_components/remote_media_player/const.py

@@ -8,11 +8,14 @@ CONF_PORT = "port"
 CONF_TOKEN = "token"
 CONF_POLL_INTERVAL = "poll_interval"
 CONF_NAME = "name"
+CONF_USE_WEBSOCKET = "use_websocket"
 
 # Default values
 DEFAULT_PORT = 8765
 DEFAULT_POLL_INTERVAL = 5
 DEFAULT_NAME = "Remote Media Player"
+DEFAULT_USE_WEBSOCKET = True
+DEFAULT_RECONNECT_INTERVAL = 30
 
 # API endpoints
 API_HEALTH = "/api/health"
@@ -27,6 +30,7 @@ API_MUTE = "/api/media/mute"
 API_SEEK = "/api/media/seek"
 API_SCRIPTS_LIST = "/api/scripts/list"
 API_SCRIPTS_EXECUTE = "/api/scripts/execute"
+API_WEBSOCKET = "/api/media/ws"
 
 # Service names
 SERVICE_EXECUTE_SCRIPT = "execute_script"