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/config/settingsCredits.ts

@@ -141,6 +141,7 @@ const CONTRIBUTOR_ENTRIES = [
       'Analytics: Opus waveform/LUFS/enrichment decode via symphonia-adapter-libopus in the analysis pipeline (PR #883)',
       'Artist page: top-track thumbnails use the same album cover path and warm batch as the albums grid (PR #886)',
       'Library browse navigation: session restore on back for Artists, Search/Tracks, New Releases, Random Albums; unified SearchBrowsePage (PR #936)',
+      'Genres: local index genre browse with Subsonic fallback, aligned counts cache, scroll restore, hold-to-shuffle play (PR #937)',
     ],
   },
   {