fix(context): fix playback context tracking bugs

Multiple critical fixes for context tracking:

1. Add 'local_library' to backend context type parser
   - Was rejecting 'local_library' causing "Invalid context type" error
   - Now properly recognized in set_playback_context command

2. Fix shuffle to not always start with first track
   - Removed logic that moved current track to front of shuffle
   - Now finds current track position in shuffled order instead
   - Shuffle is truly random, not biased to original order

3. Add missing await to all setPlaybackContext calls
   - PlaylistDetailView: await context creation
   - FavoritesView: make setFavoritesContext async + await calls
   - ArtistDetailView: await context creation
   - HomeView: await context creation
   - SearchView: await + use home_list type (search type doesn't exist)

   This fixes intermittent context tracking (race condition)

Fixes: shuffle starting with first song, Local Library context error,
intermittent playlist/favorites/artist/home/search context tracking

cc

src/lib/components/views/HomeView.svelte

@@ -357,8 +357,8 @@
     // Create continue listening context
     if (continueTracks.length > 0) {
       const trackIds = continueTracks.map(t => t.id);
-      
-      setPlaybackContext(
+
+      await setPlaybackContext(
         'home_list',
         'continue_listening',
         'Continue Listening',