feat(slint): A-Z alpha index for the Artists sidepanel left list

The sidepanel left artist list is now always A-Z grouped (derive_artists
groups when group-enabled OR view-mode==sidepanel; the view toggle re-derives)
with letter headers, and an AlphaStrip on its right edge jumps the list
Flickable proportionally (same approach as the album grouping — not exact,
by design). Replaces the flat ListView.

cc

crates/qbz-slint/src/favorites.rs

@@ -630,7 +630,10 @@ pub fn derive_artists(window: &AppWindow) {
     let state = window.global::<FavoritesState>();
     let query_owned = state.get_artists_search().to_lowercase();
     let query = query_owned.trim();
-    let group = state.get_artists_group_enabled();
+    // The sidepanel left list is ALWAYS A-Z grouped (independent of the grid
+    // group toggle), so it shows letter headers + the alpha jump strip.
+    let group = state.get_artists_group_enabled()
+        || state.get_artists_view_mode().as_str() == "sidepanel";
     let all = state.get_artists();
 
     // Flat (search-filtered) model. Share `all` when no query so artwork

crates/qbz-slint/src/main.rs

@@ -4403,6 +4403,9 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
                     if v == "grid" {
                         st.set_selected_artist_id("".into());
                     }
+                    // Rebuild grouped/alpha for the new mode (the sidepanel
+                    // left list is always grouped).
+                    favorites::derive_artists(&w);
                     favorites_prefs::save(&w);
                 }
             });

crates/qbz-slint/ui/favorites/FavoritesView.slint

@@ -1368,20 +1368,48 @@ export component FavoritesView inherits Rectangle {
                 padding-top: 16px;
                 spacing: 0px;
 
-                // LEFT: the favorites artist list (self-scrolling).
+                // LEFT: the favorites artist list, A-Z grouped, with a
+                // proportional alpha jump strip (like the album grouping).
                 Rectangle {
                     width: 300px;
-                    ListView {
-                        width: 100%;
-                        height: 100%;
-                        for artist[i] in FavoritesState.artists-visible: SidepanelArtistRow {
-                            item: artist;
-                            selected: FavoritesState.selected-artist-id == artist.id;
-                            clicked(id, name) => {
-                                FavoritesActions.select-artist(id, name);
+                    clip: true;
+                    left-flick := Flickable {
+                        viewport-width: self.width;
+                        viewport-height: left-col.preferred-height;
+                        left-col := VerticalLayout {
+                            width: parent.width;
+                            padding-top: 4px;
+                            padding-bottom: 40px;
+                            padding-right: 22px;
+                            spacing: 4px;
+                            alignment: start;
+                            for section[s] in FavoritesState.artists-grouped: VerticalLayout {
+                                spacing: 2px;
+                                Text {
+                                    text: section.title;
+                                    color: Theme.text-secondary;
+                                    font-size: Typography.legal;
+                                    font-weight: Typography.semibold;
+                                }
+                                for artist[i] in section.artists: SidepanelArtistRow {
+                                    item: artist;
+                                    selected: FavoritesState.selected-artist-id == artist.id;
+                                    clicked(id, name) => {
+                                        FavoritesActions.select-artist(id, name);
+                                    }
+                                }
                             }
                         }
                     }
+                    if FavoritesState.artists-alpha.length > 0: AlphaStrip {
+                        x: parent.width - self.width - 2px;
+                        height: 100%;
+                        jumps: FavoritesState.artists-alpha;
+                        jump(ord, idx) => {
+                            left-flick.viewport-y = -(ord / Math.max(1, FavoritesState.artists-alpha.length - 1))
+                                * Math.max(0, (left-flick.viewport-height - left-flick.height) / 1px) * 1px;
+                        }
+                    }
                 }
                 Rectangle {
                     width: 1px;