feat(qbz-slint): RadioCard 200px + hover-reveal scrollbar base

- RadioCard enlarged to 200x246 to match Album/Playlist cards; ForYouView +
  Spotlight row-width math updated to 200.
- Scrollbar hover-reveal: ListScrollbar gains a reveal prop (default true, no
  regression) and fades on opacity; TrackRow exposes hover-changed; AlbumPageView
  wired as the verified template (row-hover count -> reveal).

cc

crates/qbz-slint/ui/album/AlbumPageView.slint

@@ -117,6 +117,10 @@ export component AlbumPageView inherits Rectangle {
     callback open-artist(string);
     callback media-action(string, string, string);
 
+    // Count of track rows currently hovered (>0 = pointer over the list) — the
+    // hover-reveal source for the scrollbar (sidebar pattern).
+    property <int> scroll-hover-rows: 0;
+
     // Whether the full-description modal is open.
     property <bool> show-description: false;
 
@@ -599,6 +603,11 @@ export component AlbumPageView inherits Rectangle {
                         media-action(kind, id, action) => {
                             root.media-action(kind, id, action);
                         }
+                        hover-changed(h) => {
+                            root.scroll-hover-rows = h
+                                ? root.scroll-hover-rows + 1
+                                : Math.max(0, root.scroll-hover-rows - 1);
+                        }
                     }
                 }
 
@@ -637,7 +646,8 @@ export component AlbumPageView inherits Rectangle {
         }
     }
 
-    // Shared scrollbar in the right gutter (homologated cross-view).
+    // Shared scrollbar in the right gutter (homologated cross-view). Hover-
+    // reveal: shown while the pointer is over the track rows (or the gutter).
     ListScrollbar {
         x: parent.width - self.width - 4px;
         width: 14px;
@@ -645,6 +655,7 @@ export component AlbumPageView inherits Rectangle {
         viewport-height: flick.viewport-height;
         visible-height: flick.height;
         viewport-y <=> flick.viewport-y;
+        reveal: root.scroll-hover-rows > 0;
     }
 
     // --- Full-description modal --------------------------------------------

crates/qbz-slint/ui/discover/ForYouView.slint

@@ -74,7 +74,7 @@ export component ForYouView inherits VerticalLayout {
             radio-flick := Flickable {
                 width: 100%;
                 height: parent.height;
-                viewport-width: ForYouState.radio-stations.length * (180px + 32px);
+                viewport-width: ForYouState.radio-stations.length * (200px + 32px);
                 viewport-height: self.height;
                 HorizontalLayout {
                     spacing: 32px;

crates/qbz-slint/ui/discover/RadioCard.slint

@@ -20,24 +20,25 @@ export component RadioCard inherits Rectangle {
     callback clicked();
     callback play();
 
-    width: 180px;
-    height: 234px;
+    // Matches AlbumCard / PlaylistCard (200 x 246): panel 200 + 8 + meta.
+    width: 200px;
+    height: 246px;
 
     VerticalLayout {
         spacing: 8px;
 
         // Display panel.
         panel := Rectangle {
-            width: 180px;
-            height: 180px;
+            width: 200px;
+            height: 200px;
             border-radius: Radius.sm;
             background: Theme.surface-elevated;
             clip: true;
 
             // Centered artwork "display".
             Rectangle {
-                width: 114px;
-                height: 114px;
+                width: 126px;
+                height: 126px;
                 x: (parent.width - self.width) / 2;
                 y: (parent.height - self.height) / 2 - 8px;
                 border-radius: 4px;
@@ -110,14 +111,14 @@ export component RadioCard inherits Rectangle {
             font-size: Typography.body;
             font-weight: Typography.medium;
             overflow: elide;
-            width: 180px;
+            width: 200px;
         }
         if root.seed-subtitle != "": Text {
             text: root.seed-subtitle;
             color: Theme.text-muted;
             font-size: Typography.legal;
             overflow: elide;
-            width: 180px;
+            width: 200px;
         }
     }
 }

crates/qbz-slint/ui/discover/Spotlight.slint

@@ -45,10 +45,10 @@ export component Spotlight inherits VerticalLayout {
     callback media-action(string, string, string);
 
     property <length> gap: 24px;
-    // Row content width: TopTracks(180) + Radio(180) + albums(220 each)
+    // Row content width: TopTracks(200) + Radio(200) + albums(200 each)
     // + gaps. has-top-tracks toggles the first card.
     property <length> radio-cards-width:
-        (ForYouState.spotlight-has-top-tracks ? 180px + root.gap : 0px) + 180px + root.gap;
+        (ForYouState.spotlight-has-top-tracks ? 200px + root.gap : 0px) + 200px + root.gap;
     property <int> album-count: ForYouState.spotlight-albums.length;
     property <length> content-width:
         root.radio-cards-width

crates/qbz-slint/ui/primitives/ListScrollbar.slint

@@ -11,9 +11,18 @@ export component ListScrollbar inherits Rectangle {
     in property <length> viewport-height;
     in property <length> visible-height;
     in-out property <length> viewport-y;
+    // Hover-reveal: the owning view sets this true while the pointer is over the
+    // scrollable rows; the bar also reveals on its own gutter hover/drag. When
+    // false it fades out. DEFAULTS TRUE so views that don't wire it keep the bar
+    // always visible (no behaviour change until a view opts in).
+    in property <bool> reveal: true;
 
     // Only meaningful when the content overflows.
     property <length> max-scroll: max(0px, root.viewport-height - root.visible-height);
+
+    // Fade out unless revealed (by row hover) or the gutter itself is engaged.
+    opacity: (root.reveal || bar-ta.has-hover || bar-ta.pressed) ? 1.0 : 0.0;
+    animate opacity { duration: 150ms; }
     property <length> thumb-h:
         root.viewport-height > 0px
             ? max(48px, root.visible-height / root.viewport-height * root.height)

crates/qbz-slint/ui/primitives/TrackRow.slint

@@ -47,12 +47,20 @@ export component TrackRow inherits Rectangle {
     // Whether the row can be dragged onto sidebar playlists.
     in property <bool> draggable: true;
     callback media-action(string, string, string);
+    // Reports the row's overall hover state so a list view can reveal its
+    // scrollbar while the pointer is anywhere over the rows (the proven sidebar
+    // pattern — a background/Flickable-level TouchArea can't see hover over a
+    // row's own touch areas).
+    callback hover-changed(bool);
 
     // Explicit track number, else the 1-based list position.
     property <string> number-text:
         root.track.number != "" ? root.track.number : "\{root.index + 1}";
     property <bool> row-hovered:
         ta.has-hover || play-cell.hovered || more-ta.has-hover;
+    changed row-hovered => {
+        root.hover-changed(self.row-hovered);
+    }
 
     height: 50px;
     border-radius: 8px;