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/src/lib.rs

@@ -707,6 +707,7 @@ pub fn run() {
             psysonic_library::commands::library_live_search,
             psysonic_library::commands::library_advanced_search,
             psysonic_library::commands::library_list_lossless_albums,
+            psysonic_library::commands::library_list_albums_by_genre,
             psysonic_library::commands::library_get_artist_lossless_browse,
             psysonic_library::commands::library_search_cross_server,
             psysonic_library::commands::library_get_track,
@@ -727,6 +728,7 @@ pub fn run() {
             psysonic_library::commands::library_patch_track,
             psysonic_library::browse_support::library_reconcile_album_stars,
             psysonic_library::browse_support::library_get_catalog_year_bounds,
+            psysonic_library::browse_support::library_get_genre_album_counts,
             psysonic_library::commands::library_put_artifact,
             psysonic_library::commands::library_put_fact,
             psysonic_library::commands::library_record_play_session,