feat(slint): extend scroll-position restore to all views

Wire the per-history-entry scroll memory (added for Local Library) into
every top-level view: Home/Discover, Album, Local Album, Artist, Musician,
Label, Label Releases, Location, Favorites, Mix, Playlist, Playlist Manager,
Offline Manager, Search, Settings.

Each view's primary scroll container reports its viewport-y and restores it
on back/forward via NavState.restore-scope (scope_for in main.rs maps each
entry to a stable id; tab views carry the tab, e.g. "fav:albums"). The
container restores once per arm, only after content lays out, then clears
the scope. A `changed sr-armed` trigger covers views that persist across
sub-tab navigation (Home's Discover tabs, Favorites' shared list, Playlist
A->B->A) where no fresh mount occurs.

ScrollView-based views (Offline Manager, Settings) use visible-height for
the overflow check; ListView/Flickable views use height. Favorites' shared
albums/artists/playlists/labels Flickable matches the active tab's scope
dynamically.

cc

crates/qbz-slint/ui/playlist/PlaylistManagerView.slint

@@ -18,6 +18,7 @@ import {
     PmFolderItem,
     PmPlaylistItem,
     PmTreeRow,
+    NavState,
 } from "../state.slint";
 import { QbzIcon } from "../primitives/QbzIcon.slint";
 import { LoadingSpinner } from "../primitives/LoadingSpinner.slint";
@@ -1233,6 +1234,18 @@ export component PlaylistManagerView inherits Rectangle {
             vertical-stretch: 1;
             viewport-width: self.width;
             viewport-height: page.preferred-height;
+            // Scroll-position restore on back/forward (see nav::scope_for).
+            property <string> sr-armed: NavState.restore-scope;
+            function sr-restore() {
+                if (NavState.restore-scope == "playlist-manager" && self.viewport-height > self.height) {
+                    self.viewport-y = NavState.scroll-restore;
+                    NavState.restore-scope = "";
+                }
+            }
+            init => { self.sr-restore(); }
+            changed sr-armed => { self.sr-restore(); }
+            changed viewport-height => { self.sr-restore(); }
+            changed viewport-y => { NavState.report-scroll(self.viewport-y); }
 
             page := VerticalLayout {
                 width: parent.width;

crates/qbz-slint/ui/playlist/PlaylistView.slint

@@ -6,7 +6,7 @@
 import { Theme } from "../foundation/semantic-colors.slint";
 import { Typography } from "../foundation/typography.slint";
 import { Radius } from "../foundation/radius.slint";
-import { PlaylistState, PlaylistActions, DragState } from "../state.slint";
+import { PlaylistState, PlaylistActions, DragState, NavState } from "../state.slint";
 import { QbzIcon } from "../primitives/QbzIcon.slint";
 import { TrackRow } from "../primitives/TrackRow.slint";
 import { ExpandableSearch } from "../primitives/ExpandableSearch.slint";
@@ -625,6 +625,18 @@ export component PlaylistView inherits Rectangle {
                     track-list := ListView {
                         vertical-stretch: 1;
                         vertical-scrollbar-policy: ScrollBarPolicy.always-off;
+                        // Scroll-position restore on back/forward (see nav::scope_for).
+                        property <string> sr-armed: NavState.restore-scope;
+                        function sr-restore() {
+                            if (NavState.restore-scope == "playlist" && self.viewport-height > self.height) {
+                                self.viewport-y = NavState.scroll-restore;
+                                NavState.restore-scope = "";
+                            }
+                        }
+                        init => { self.sr-restore(); }
+                        changed sr-armed => { self.sr-restore(); }
+                        changed viewport-height => { self.sr-restore(); }
+                        changed viewport-y => { NavState.report-scroll(self.viewport-y); }
                         for track[i] in PlaylistState.tracks: TrackRow {
                             track: track;
                             index: i;