feat(qbz-slint): album card hover overlay

Album cards gain the AlbumCardLite-style hover overlay: a dark scrim,
genre/year meta in the top-left, and circular favorite / play / more
action buttons (play primary, white). The action buttons are visual
for now; one TouchArea over the artwork drives the hover state and
emits a clicked(album_id) callback for navigation.

AlbumCardItem carries genre and year; home.rs maps them from the
discover album (genre name, year from the release dates).

cc

crates/qbz-slint/ui/state.slint

@@ -7,6 +7,8 @@ export struct AlbumCardItem {
     id: string,
     title: string,
     artist: string,
+    genre: string,         // shown in the hover overlay
+    year: string,          // shown in the hover overlay
     quality-tier: string,  // "hires" | "cd" | "" — drives the badge icon
     ribbon: string,
     ribbon-kind: string,   // "press" | "qobuzissime" | "albumOfTheWeek" | ""