feat(genres): local index genre browse with Subsonic fallback (#937)

* feat(genres): genre detail browse via local index with aligned counts

Move genre detail albums/play/shuffle onto the local library index with
Albums-style in-page scroll, session restore, and genre-scoped stash. Unify
genre album totals between the cloud and detail pages via
library_get_genre_album_counts, and fix grouped browse totals to count
distinct albums rather than matching tracks.

* perf(genres): local genre browse with scoped counts cache

Add dedicated Rust genre album pagination and indexes, slice-mode grid
loading, library-filter-aware counts, and a long-lived in-memory catalog
cache invalidated on sync so genre pages avoid repeated full-library SQL.

* fix(genres): restore scroll after album back; play hold-to-shuffle

Pin restore display count in refs so clearing the return stash no longer
reloads the genre grid mid-restore. Load the first SQL page only (60 rows),
use long-press on Play for shuffle, and add genre play tooltips.

* fix(genres): fall back to Subsonic byGenre when local index unavailable

Genre detail album grid now matches All Albums: try library_list_albums_by_genre
first, then getAlbumsByGenre when the index is off, not ready, or errors.

* docs: add CHANGELOG and credits for PR #937

src-tauri/crates/psysonic-library/src/commands.rs

@@ -482,6 +482,16 @@ pub async fn library_list_lossless_albums(
     library_spawn_blocking(move || crate::lossless_albums::list_lossless_albums(&store, &request)).await
 }
 
+#[tauri::command]
+pub async fn library_list_albums_by_genre(
+    runtime: State<'_, LibraryRuntime>,
+    request: crate::dto::LibraryGenreAlbumsRequest,
+) -> Result<crate::dto::LibraryGenreAlbumsResponse, String> {
+    let store = Arc::clone(&runtime.store);
+    library_spawn_blocking(move || crate::genre_album_browse::list_albums_by_genre(&store, &request))
+        .await
+}
+
 #[tauri::command]
 pub async fn library_get_artist_lossless_browse(
     runtime: State<'_, LibraryRuntime>,