fix(library): integrate navigation history for back/forward support

Mouse back/forward buttons now work in local library view.

Changes:
- Add 'library-album' ViewType to navigation store
- Add selectLocalAlbum(), clearLocalAlbum(), getSelectedLocalAlbumId()
- LocalLibraryView subscribes to navigation state changes
- Album clicks use selectLocalAlbum() for proper history tracking
- Back button uses navGoBack() to navigate properly
- Tab changes navigate back to 'library' when viewing album
- +page.svelte shows LocalLibraryView for both 'library' and 'library-album'

cc

src/routes/+page.svelte

@@ -1765,7 +1765,7 @@
           onTrackGoToArtist={handleArtistClick}
           onPlaylistClick={selectPlaylist}
         />
-      {:else if activeView === 'library'}
+      {:else if activeView === 'library' || activeView === 'library-album'}
         <LocalLibraryView
           onTrackPlay={handleLocalTrackPlay}
           onTrackPlayNext={queueLocalTrackNext}