feat(locallibrary): local album detail (reuses AlbumPageView)

Clicking a local album (grid card or a track row's album link) opens its
detail in the shared AlbumPageView. navigate_local_album loads the album's
metadata-grouped tracks (get_album_tracks_metadata) + fills folder covers,
populates AlbumState (title / album-artist or "Various Artists" / cover /
quality / "N tracks · duration" / disc-ordered TrackRows) with a new is-local
flag, and resolves the cover from disk. Play routes to local: the media-action
dispatcher gains a guard — when the album view shows a local album, album play
-> play_local_album, a track row -> play the album from that track; Qobuz
album/track play is untouched (guarded by view==Album && is-local).

cc

crates/qbz-slint/ui/state.slint

@@ -288,6 +288,9 @@ export global AlbumState {
     in property <[string]> awards: [];
     in property <[TrackItem]> tracks: [];
     in property <bool> loading: false;
+    // True when this is a Local Library album (local files / offline copies).
+    // Routes the play actions to local playback + hides Qobuz-only chrome.
+    in property <bool> is-local: false;
 }
 
 // Album-view actions wired to Rust callbacks.