feat: shared DisplayCoordinator + optional API token

- Introduce DisplayCoordinator polling /api/display/monitors once per
  cycle and fan out to all per-display entities via CoordinatorEntity.
  Removes ~9x redundant requests per polling cycle that came from each
  binary_sensor/number/select/sensor/switch entity calling
  get_display_monitors() in its own async_update.
- Optimistic write-through via coordinator.apply_optimistic(...) keeps
  sibling entities in sync after slider/select writes without an extra
  network round-trip.
- Make CONF_TOKEN optional. The media server already supports running
  without auth (auth_enabled() returns False when api_tokens is empty),
  so the integration omits the Authorization header and ?token= query
  from REST/WS/album-art URLs when no token is configured. Server-side
  auth-enabled rejections still surface as invalid_auth in the UI.
- Bump manifest version to 0.3.2.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

custom_components/remote_media_player/config_flow.py

@@ -44,10 +44,14 @@ async def validate_input(hass: HomeAssistant, data: dict[str, Any]) -> dict[str,
         CannotConnect: If connection fails
         InvalidAuth: If authentication fails
     """
+    # Token is optional: the media server can run without auth tokens, in which
+    # case verify_token() returns "anonymous" and accepts unauthenticated calls.
+    # If the server *does* have tokens configured, get_status() below will 401
+    # and we surface that as "invalid_auth" in the UI.
     client = MediaServerClient(
         host=data[CONF_HOST],
         port=data[CONF_PORT],
-        token=data[CONF_TOKEN],
+        token=data.get(CONF_TOKEN, "") or "",
     )
 
     try:
@@ -125,7 +129,7 @@ class ConfigFlow(config_entries.ConfigFlow, domain=DOMAIN):
                             mode=selector.NumberSelectorMode.BOX,
                         )
                     ),
-                    vol.Required(CONF_TOKEN): selector.TextSelector(
+                    vol.Optional(CONF_TOKEN, default=""): selector.TextSelector(
                         selector.TextSelectorConfig(
                             type=selector.TextSelectorType.PASSWORD
                         )