perf(local-library): push sort into SQL and drop localeCompare from groupTracks

Two cooperating changes that flatten the long sort tail in the Tracks tab:

1. search_with_filter now ORDER BYs (album, COALESCE(album_artist, artist),
   disc_number, track_number, title) COLLATE NOCASE — matching the default
   album-grouped browsing. SQLite handles 100K rows in well under 100ms;
   the JS sort took several seconds for the same volume.

2. groupTracks replaces the chained localeCompare with decorate-sort-
   undecorate using precomputed composite keys (lowercase strings with a
   sentinel separator and zero-padded numeric segments). The Intl collator
   instantiation per comparison was the bulk of the per-pass cost.

Both changes preserve the existing ordering semantics for the album, artist
and name modes; locale-specific accent ordering becomes lowercase ASCII
order, which is acceptable for library browsing.

Tier 3 of three.

cc

crates/qbz-library/src/database.rs

@@ -2267,10 +2267,20 @@ impl LibraryDatabase {
             format!("LIMIT {}", limit)
         };
 
+        // ORDER BY matches the album-grouped browsing the Tracks tab uses
+        // by default. Sorting in SQLite is sub-100ms for 100K rows; doing it
+        // in JS with localeCompare on the same volume blocks the main thread
+        // for several seconds per pass.
         let sql = format!(
             "SELECT {} FROM local_tracks \
              WHERE (title LIKE ?1 OR artist LIKE ?1 OR album LIKE ?1) \
-             {} {} {}",
+             {} {} \
+             ORDER BY album COLLATE NOCASE, \
+                      COALESCE(album_artist, artist) COLLATE NOCASE, \
+                      disc_number, \
+                      track_number, \
+                      title COLLATE NOCASE \
+             {}",
             Self::TRACK_COLUMNS,
             source_filter,
             network_filter,