refactor(m3u): add loading state for channel list and improve playlist handling

- Implemented a loading state for channel lists in various components, enhancing user experience during data fetching.
- Added `ChannelListLoadingStateComponent` to display loading skeletons for channels and groups.
- Updated `M3uWorkspaceRouteSession` to manage loading states more effectively when fetching playlists.
- Modified `VideoPlayerComponent`, `SidebarComponent`, and `ChannelListContainerComponent` to utilize the new loading state.
- Enhanced tests to cover new loading behaviors and ensure proper dispatching of loading actions.

docs/architecture/m3u-playlist-module.md

@@ -49,6 +49,9 @@ interface PlaylistState {
     // Active channel being played
     active: Channel | undefined;
 
+    // Whether the current route is still resolving channel data
+    channelsLoading: boolean;
+
     // All channels from current playlist
     channels: Channel[];
 
@@ -85,6 +88,7 @@ interface PlaylistState {
 ```typescript
 // Channel selectors
 selectActive          // Current playing channel
+selectChannelsLoading // Channel list loading flag
 selectChannels        // All channels array
 selectFavorites       // Favorite channel URLs
 
@@ -165,6 +169,18 @@ channel-list-container/
               ChannelActions.setActiveChannel
 ```
 
+### Loading States
+
+- `M3uWorkspaceRouteSession` owns route-driven channel loading for the player/sidebar routes: `all` and `groups`.
+- The route session sets `channelsLoading` before `getPlaylist()` resolves and clears it when `ChannelActions.setChannels` lands.
+- `ChannelListContainerComponent` now renders a dedicated skeleton state while `channelsLoading` is true.
+- `ChannelListContainerComponent` no longer clears `channels` on destroy; route/session code is the single owner of shared list lifecycle during navigation.
+- The dedicated `/workspace/playlists/:id/favorites` and `/workspace/playlists/:id/recent` collection routes do not drive the shared sidebar channel list; they default to the `playlist` scope so rail links always open the current playlist view, not the last persisted global scope.
+- Empty playlists and empty search results are no longer conflated:
+  - loading: skeletons
+  - empty source: no channels in the playlist after loading completes
+  - empty search: no matches within an already loaded playlist
+
 ### EnrichedChannel Pattern
 
 For performance optimization, channels are pre-enriched with EPG data: