feat: remember scroll + search position on Back (web + android)

Going into an album/artist and back now restores the scroll position and
keeps the typed query, instead of resetting to the top.

- Web: navigation.js snapshots each history entry's #main-content scroll and
  any open local (header) search, restoring them on Back/Forward; a genuine
  new navigation still starts at the top.
- Android: the Alben/Künstler lists (LibraryViewModel) and the global/local
  search-results lists (ExploreViewModel/SearchViewModel) hoist their
  LazyListState/LazyGridState, so scroll survives a drill-in/back for the
  tab's lifetime.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CHANGELOG.md

@@ -89,6 +89,15 @@ like Android), concert events become **reliable across web/Android**, several An
 - **30s preview in the importer (Android)** — each resolved track now has a ▶/⏹ button that plays its
   Deezer/Spotify preview clip through the same app-level preview bar as Explore (library playback
   pauses; the row highlights while playing). Parity with the web importer.
+- **Scroll & search position remembered on Back (Web + Android)** — going into an album/artist and
+  back now returns you to the same scroll spot with your typed query still there, instead of jumping
+  to the top. Web: each history entry's scroll (and the open local/header search) is snapshotted and
+  restored on Back/Forward; a genuine new navigation still starts at the top. Android: the Alben /
+  Künstler lists and the global/local search-results scroll are hoisted into their ViewModels, so
+  they survive a drill-in/back for as long as you're in that tab.
+- **Partial album — Play / Shuffle + track menu (Android)** — an incomplete album's downloaded
+  tracks now have **Abspielen** and **Zufall** buttons and a per-row 3-dot menu, so you can still
+  play/shuffle what you have while the rest downloads.
 - **Swipe between tabs (Android)** — a left/right swipe now switches tabs in **Now Playing**
   (Player ↔ Lyrics ↔ Queue) and in the **Bibliothek** (Playlists ↔ Alben ↔ Künstler ↔ Offline),
   two-way synced with the tab bar, matching the existing Erkunden swipe. On Now Playing the cover's