feat(playlists): expose scene playlists as Home Assistant entities

One device per scene playlist (model "Scene Playlist"), each with:
- a switch (start/stop; the server cycles one playlist at a time, so starting one stops any other)
- a "Current Scene" sensor that resolves the active preset name from scene_presets while this playlist is cycling
- an "Items" diagnostic sensor (configured scene count; no state_class)

The coordinator reads scene_playlists plus the flat playlist_state from the /api/v1/snapshot payload and gains start_playlist()/stop_playlist(); __init__ registers and prunes per-playlist devices and reloads on playlist-id changes; the event listener also refreshes on the playlist_state_changed WS event. Shared device/lookup/running-state plumbing lives in a new LedGrabPlaylistEntity base (entity.py) used by both the switch and the sensors. Adds en/ru translation keys.

Note: this also lands the in-progress coordinator migration from the per-request fan-out to the single /api/v1/snapshot poll that was already present in the working tree.

Requires the led-grab server /api/v1/snapshot to emit scene_playlists + playlist_state (companion server change, tracked separately).

custom_components/ledgrab/sensor.py

@@ -29,6 +29,7 @@ from .const import (
     DATA_COORDINATOR,
 )
 from .coordinator import LedGrabCoordinator
+from .entity import LedGrabPlaylistEntity
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -59,6 +60,14 @@ async def async_setup_entry(
         for clock in coordinator.data.get("sync_clocks", []):
             entities.append(SyncClockElapsedSensor(coordinator, clock["id"], entry.entry_id))
 
+        for playlist in coordinator.data.get("scene_playlists", []):
+            entities.append(
+                PlaylistCurrentSceneSensor(coordinator, playlist["id"], entry.entry_id)
+            )
+            entities.append(
+                PlaylistItemsSensor(coordinator, playlist["id"], entry.entry_id)
+            )
+
     entities.extend(_build_server_sensors(coordinator, entry.entry_id))
 
     async_add_entities(entities)
@@ -268,6 +277,93 @@ class SyncClockElapsedSensor(CoordinatorEntity, SensorEntity):
         return None
 
 
+class _PlaylistSensorBase(LedGrabPlaylistEntity, SensorEntity):
+    """Sensor attached to a scene-playlist device.
+
+    Device/availability/lookup plumbing lives in :class:`LedGrabPlaylistEntity`
+    so it stays in sync with the playlist switch.
+    """
+
+
+class PlaylistCurrentSceneSensor(_PlaylistSensorBase):
+    """Name of the scene preset this playlist is currently holding.
+
+    Only this playlist's value populates while it is the active (cycling) one;
+    every other playlist's sensor reads ``None`` (idle). The value advances as
+    the engine steps to the next item.
+    """
+
+    _attr_icon = "mdi:playlist-star"
+
+    def __init__(
+        self,
+        coordinator: LedGrabCoordinator,
+        playlist_id: str,
+        entry_id: str,
+    ) -> None:
+        super().__init__(coordinator, playlist_id, entry_id)
+        self._attr_unique_id = f"{playlist_id}_current_scene"
+        self._attr_translation_key = "playlist_current_scene"
+
+    @property
+    def native_value(self) -> str | None:
+        state = self._running_state()
+        if not state:
+            return None
+        preset_id = state.get("current_preset_id")
+        if not preset_id:
+            return None
+        return self._resolve_preset_name(preset_id)
+
+    @property
+    def extra_state_attributes(self) -> dict[str, Any]:
+        state = self._running_state()
+        if not state:
+            return {}
+        return {
+            "current_preset_id": state.get("current_preset_id"),
+            "current_index": state.get("current_index"),
+            "item_count": state.get("item_count"),
+        }
+
+    def _resolve_preset_name(self, preset_id: str) -> str:
+        """Map a scene-preset id to its display name (fall back to the id)."""
+        if self.coordinator.data:
+            for preset in self.coordinator.data.get("scene_presets", []):
+                if preset.get("id") == preset_id:
+                    return preset.get("name", preset_id)
+        return preset_id
+
+
+class PlaylistItemsSensor(_PlaylistSensorBase):
+    """Number of scene presets queued in a playlist (static config stat).
+
+    No ``state_class`` — this is a configuration cardinality that only changes
+    when the playlist is edited, so it shouldn't be enrolled in long-term
+    statistics.
+    """
+
+    _attr_icon = "mdi:playlist-music"
+    _attr_entity_category = EntityCategory.DIAGNOSTIC
+
+    def __init__(
+        self,
+        coordinator: LedGrabCoordinator,
+        playlist_id: str,
+        entry_id: str,
+    ) -> None:
+        super().__init__(coordinator, playlist_id, entry_id)
+        self._attr_unique_id = f"{playlist_id}_items"
+        self._attr_translation_key = "playlist_items"
+
+    @property
+    def native_value(self) -> int | None:
+        playlist = self._get_playlist()
+        if playlist is None:
+            return None
+        return len(playlist.get("items") or [])
+
+
 class HALightMappedLightsSensor(CoordinatorEntity, SensorEntity):
     """Sensor showing the number of mapped HA lights for an HA Light target."""