feat(slint): extend QueueState model for the queue sidebar

Restructure the QueueState global so the sidebar can render two tabs and
a paginated upcoming list: separate now-playing / upcoming-page / history
properties, paginator counters, tab and search state, and callbacks for
every control. QueueItem gains duration and explicit fields. Adds a
favorite semantic color token and the heart-filled, infinity and list-x
icons the sidebar needs.

cc

crates/qbz-slint/ui/foundation/semantic-colors.slint

@@ -24,6 +24,9 @@ export global Theme {
     out property <color> accent-pressed: Palette.blue-active;
     out property <color> accent-text: Palette.white;
 
+    // Favorite (heart) — the active "loved" state.
+    out property <color> favorite: Palette.danger;
+
     // Surfaces — interaction
     out property <color> surface-hover: Palette.alpha-6;