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/utils/library/albumBrowseLoad.ts

@@ -36,10 +36,15 @@ export async function fetchLocalAlbumCatalogChunk(
   offset: number,
   chunkSize: number,
 ): Promise<AlbumBrowsePageResult | null> {
-  const limit = query.genres.length > 0 && offset === 0 ? GENRE_ALBUM_FETCH_LIMIT : chunkSize;
-  if (query.genres.length > 0 && offset > 0) {
+  const singleGenre = query.genres.length === 1;
+  if (query.genres.length > 1 && offset > 0) {
     return { albums: [], hasMore: false };
   }
+  const limit = singleGenre
+    ? chunkSize
+    : query.genres.length > 0 && offset === 0
+      ? GENRE_ALBUM_FETCH_LIMIT
+      : chunkSize;
   return runLocalAlbumBrowse(serverId, query, offset, limit);
 }