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>

android/app/src/main/kotlin/com/novasonic/app/ui/screen/ExploreScreen.kt

@@ -317,7 +317,7 @@ private fun LibrarySearchContent(
         return
     }
 
-    LazyColumn {
+    LazyColumn(state = vm.listState) {
         val artists = state.searchResult?.artist ?: emptyList()
         val albums  = state.searchResult?.album  ?: emptyList()
         val songs   = state.searchResult?.song   ?: emptyList()
@@ -461,7 +461,7 @@ private fun GlobalExploreContent(
         return
     }
 
-    LazyColumn {
+    LazyColumn(state = vm.searchListState) {
         if (state.error != null) {
             item { Text(state.error, color = MaterialTheme.colorScheme.error,
                 modifier = Modifier.padding(16.dp)) }

android/app/src/main/kotlin/com/novasonic/app/ui/screen/LibraryScreen.kt

@@ -166,7 +166,7 @@ fun LibraryScreen(
                         )
                     }
                 }
-                val albumGridState = rememberLazyGridState()
+                val albumGridState = vm.albumsGridState  // hoisted → survives album drill-in/back
                 LaunchedEffect(state.albumSort) { albumGridState.scrollToItem(0) }
                 LazyVerticalGrid(
                     state   = albumGridState,
@@ -189,7 +189,7 @@ fun LibraryScreen(
             }
 
             LibraryTab.ARTISTS -> {
-                val listState  = rememberLazyListState()
+                val listState  = vm.artistsListState  // hoisted → survives artist drill-in/back
                 val scope      = rememberCoroutineScope()
                 val letters    = remember(state.artistIndexes) { state.artistIndexes.map { it.name } }
                 // Map letter → flat LazyColumn index of its header item

android/app/src/main/kotlin/com/novasonic/app/viewmodel/ExploreViewModel.kt

@@ -10,6 +10,7 @@ import com.novasonic.app.api.model.DownloadRequest
 import com.novasonic.app.api.model.ItunesItem
 import com.novasonic.app.api.model.ItunesRssEntry
 import com.novasonic.app.api.model.Song
+import androidx.compose.foundation.lazy.LazyListState
 import com.novasonic.app.api.model.artworkHd
 import com.novasonic.app.app
 import com.novasonic.app.data.NotificationStore
@@ -76,6 +77,9 @@ class ExploreViewModel(app: Application) : AndroidViewModel(app) {
     private val _state = MutableStateFlow(ExploreUiState(chartsLoading = true))
     val state: StateFlow<ExploreUiState> = _state
 
+    // Global-search results scroll — hoisted so it survives an album/artist drill-in and back.
+    val searchListState = LazyListState()
+
     private var searchJob: Job? = null
 
     init {

android/app/src/main/kotlin/com/novasonic/app/viewmodel/LibraryViewModel.kt

@@ -1,6 +1,8 @@
 package com.novasonic.app.viewmodel
 
 import android.app.Application
+import androidx.compose.foundation.lazy.LazyListState
+import androidx.compose.foundation.lazy.grid.LazyGridState
 import androidx.lifecycle.AndroidViewModel
 import androidx.lifecycle.viewModelScope
 import com.novasonic.app.api.model.Album
@@ -34,6 +36,12 @@ class LibraryViewModel(app: Application) : AndroidViewModel(app) {
     private val _state = MutableStateFlow(LibraryUiState(isLoading = true))
     val state: StateFlow<LibraryUiState> = _state
 
+    // Scroll positions live in the VM so they survive drilling into an album/artist and back (the
+    // Library back-stack entry, hence this VM, is retained). A full teardown of the tab → fresh VM
+    // → back at the top, as expected.
+    val albumsGridState  = LazyGridState()
+    val artistsListState = LazyListState()
+
     init { loadPlaylists() }
 
     fun setAlbumSort(sort: AlbumSort) {

android/app/src/main/kotlin/com/novasonic/app/viewmodel/SearchViewModel.kt

@@ -1,6 +1,7 @@
 package com.novasonic.app.viewmodel
 
 import android.app.Application
+import androidx.compose.foundation.lazy.LazyListState
 import androidx.lifecycle.AndroidViewModel
 import androidx.lifecycle.viewModelScope
 import com.novasonic.app.api.model.ArtistOverride
@@ -28,6 +29,9 @@ class SearchViewModel(app: Application) : AndroidViewModel(app) {
     private val _state = MutableStateFlow(SearchUiState())
     val state: StateFlow<SearchUiState> = _state
 
+    // Results scroll — hoisted so it survives a drill-in/back within the search.
+    val listState = LazyListState()
+
     private var searchJob: Job? = null
 
     init {