fix(slint): album view layout and a working track search

Four album-view corrections from review:

- Explicit badge: the title row now uses `alignment: start`, so the E
  badge sits right after the track name instead of being stretched out
  to a fake column position.
- Label/awards sidebar: dropped `alignment: start` on the track/sidebar
  row — it had defeated the track list's stretch and left the sidebar
  floating mid-row with dead space. The list now stretches and the
  254px sidebar is flush right; it rides the content region inward when
  a main sidebar opens.
- Track search: now a real client-side filter — a TextInput drives the
  AlbumActions.search global callback; album.rs keeps the unfiltered
  list and filter_tracks() matches title/artist case-insensitively.
- Description modal: the Flickable is vertical-stretch bounded so long
  text scrolls, and strip_html keeps paragraph breaks as newlines.

cc

crates/qbz-slint/ui/state.slint

@@ -73,6 +73,12 @@ export global AlbumState {
     in property <bool> loading: false;
 }
 
+// Album-view actions wired to Rust callbacks.
+export global AlbumActions {
+    // Filter the visible track list by a query (client-side).
+    callback search(string);
+}
+
 // Which content view the shell shows.
 export enum ContentView { home, album, artist, settings }