refactor(slint): mix rows reuse SearchTrackRow; For You uses HomeSkeleton

Track row reuse: the mix views had a bespoke MixTrackRow with a dead
favorite/more controls (no context menu), while search / favorites /
artist already share SearchTrackRow (which has the TrackContextMenu).
Consolidated:
  - SearchTrackRow gains optional show-album (album column) +
    show-favorite (standalone heart) — off by default, so search /
    favorites rows are unchanged. SearchTrackItem gains an `album`
    field.
  - MixView drops MixTrackRow/MixTrackItem and renders SearchTrackRow
    with show-album + show-favorite. A row "play" starts the mix from
    that track; the context-menu actions (play next / queue / favorite
    / view album / view artist / ...) now bubble through media-action
    and work in the mix views too.

For You skeleton: the For You tab showed a bare spinner during its
lazy load; it now shows the same pulsing HomeSkeleton as Home (the
static Qobuz Mixes tiles stay visible above it). Editor's Picks is
served from the shared discover-index cache (Tauri parity) and shows
the skeleton during the initial load via the existing HomeView guard.

cc

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

@@ -17,7 +17,7 @@ import { ArtistCarousel } from "ArtistCarousel.slint";
 import { Spotlight } from "Spotlight.slint";
 import { QobuzMixesRow } from "QobuzMixesRow.slint";
 import { RadioCard } from "RadioCard.slint";
-import { LoadingSpinner } from "../primitives/LoadingSpinner.slint";
+import { HomeSkeleton } from "HomeSkeleton.slint";
 
 export component ForYouView inherits VerticalLayout {
     callback open-album(string);
@@ -29,16 +29,16 @@ export component ForYouView inherits VerticalLayout {
     callback start-radio-album(string);
     callback open-mix(string);
 
+    // While the first lazy load is in flight, show the same pulsing
+    // skeleton Home uses (the Qobuz Mixes tiles stay — they're static).
+    property <bool> show-skeleton:
+        ForYouState.loading
+        && ForYouState.release-watch.albums.length == 0
+        && ForYouState.top-artists.length == 0;
+
     spacing: 40px;
     alignment: start;
 
-    if ForYouState.loading
-        && ForYouState.release-watch.albums.length == 0
-        && ForYouState.top-artists.length == 0: HorizontalLayout {
-        alignment: center;
-        LoadingSpinner { size: 36px; }
-    }
-
     // 0. Qobuz Mixes (static navigation tiles).
     QobuzMixesRow {
         open-mix(which) => {
@@ -46,6 +46,8 @@ export component ForYouView inherits VerticalLayout {
         }
     }
 
+    if root.show-skeleton: HomeSkeleton { }
+
     // 1. Release Watch.
     if ForYouState.release-watch.albums.length > 0: Carousel {
         section: ForYouState.release-watch;