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>

src/views/navigation.js

@@ -8,6 +8,7 @@ import { loadHomeData, loadAlbumRow, loadArtists, loadAlbums, loadGenreDetail }
 import { loadArtistDetail, loadArtistAllSongs, loadAlbumDetail, loadDeezerAlbumDetail, loadPartialAlbumDetail } from './detail.js';
 import { loadPlaylists, loadPlaylistDetail, loadStarred, loadRandom } from './playlists.js';
 import { loadNewReleases, loadRecommendations } from './discover.js';
+import { onHeaderSearch } from './search.js';
 import { invalidateApiCache } from '../api.js';
 
 // ─── NAVIGATION HISTORY ───
@@ -59,13 +60,39 @@ export function refreshCurrentView() {
 }
 
 export function navigate(page, data=null) {
+  // Scroll + search memory: remember where each history entry was scrolled AND any open local
+  // (header) search, so Back/Forward returns you to the same spot with the same query. The global
+  // search page keeps its query/results on its own (its DOM persists). A genuine new navigation
+  // still starts at the top with a clean header search. On a genuine nav we snapshot the OUTGOING
+  // view here (cursor still points at it); on Back/Forward the snapshot is taken in _navOnPopState.
+  const _main    = document.getElementById('main-content');
+  const _hsInput = document.getElementById('header-search-input');
+  S._scrollByIdx = S._scrollByIdx || {};
+  S._hsByIdx     = S._hsByIdx || {};
+  if(!S._navJumping) {
+    if(_main) S._scrollByIdx[S._navCursor] = _main.scrollTop;
+    S._hsByIdx[S._navCursor] = _hsInput?.value?.trim() ? _hsInput.value : '';
+  }
   closeHeaderSearch();
+
   document.querySelectorAll('.page').forEach(p => p.classList.remove('active'));
   document.querySelectorAll('.nav-item,.bnav-item').forEach(n => n.classList.remove('active','active-blue'));
   const cls = ['discover','new-releases','recommendations'].includes(page) ? 'active-blue' : 'active';
   document.querySelectorAll(`[data-page="${page}"]`).forEach(el => el.classList.add(cls));
   const pageEl = document.getElementById(`page-${page}`);
-  if(pageEl) { pageEl.classList.add('active'); document.getElementById('main-content').scrollTop = 0; }
+  if(pageEl) {
+    pageEl.classList.add('active');
+    if(S._navJumping) {
+      // Back/Forward → restore this entry's saved scroll (rAF so the shown page has laid out) and
+      // re-open the local (header) search if one was active here.
+      const y = S._scrollByIdx[S._navCursor] || 0;
+      if(_main) requestAnimationFrame(() => { _main.scrollTop = y; });
+      const hsq = S._hsByIdx[S._navCursor];
+      if(hsq && _hsInput) { _hsInput.value = hsq; onHeaderSearch(hsq); }
+    } else if(_main) {
+      _main.scrollTop = 0;
+    }
+  }
   closeSidebar();
   if(['discover','new-releases','recommendations','random'].includes(page)) switchNavMode('discover');
   else if(['home','artists','albums','starred','playlists'].includes(page)) switchNavMode('library');
@@ -133,6 +160,13 @@ export function _navOnPopState(state) {
   }
   const idx = (state && typeof state.nsIdx === 'number') ? state.nsIdx : 0;
   if(idx < 0 || idx >= S._navStack.length) return;
+  // Snapshot the OUTGOING view's scroll + any open local search before we move the cursor.
+  const _main    = document.getElementById('main-content');
+  const _hsInput = document.getElementById('header-search-input');
+  S._scrollByIdx = S._scrollByIdx || {};
+  S._hsByIdx     = S._hsByIdx || {};
+  if(_main) S._scrollByIdx[S._navCursor] = _main.scrollTop;
+  S._hsByIdx[S._navCursor] = _hsInput?.value?.trim() ? _hsInput.value : '';
   S._navCursor = idx;
   const entry = S._navStack[idx];
   _navSave();