feat(flutter): cosmetic reveal animations (Slice F)

Final slice of the per-item rendering pass. Wraps every tile widget
in an AnimatedSwitcher between the skeleton placeholder and the real
card. 220ms cross-fade with easeOut: tiles "settle into place"
rather than hard-cutting from shimmer to content. Since each tile
fades independently as its data lands — and the HydrationQueue's
concurrency cap drains in a natural cascade — the overall feel is
the staged "page builds piece by piece" effect we wanted, with no
per-tile position math required.

Bumps CachedNetworkImage fadeInDuration from zero to 120ms (server_
image.dart, discover_screen.dart). Imperceptible on cache hits since
the image decodes synchronously; on cache misses the bytes fade in
smoothly instead of popping. Slice 1's "zero fade" call was right
about the 500ms default being a regression, but 120ms threads the
needle.

Playlist detail wraps its body in the same AnimatedSwitcher so the
cold-load skeleton page cross-fades into the real track list.

Tiles affected: home _AlbumTile / _ArtistTile / _TrackTile + liked
_LikedAlbumTile / _LikedArtistTile / _LikedTrackRow + playlist
_SkeletonBody / _Body. All keyed via ValueKey so AnimatedSwitcher
detects the transition.

End of the per-item pass. Net behavior: cold visits paint shaped
pages instantly with skeletons, content cascades in as hydration
lands; warm visits paint fully from drift in the first frame.

flutter_client/lib/library/library_screen.dart

@@ -631,6 +631,11 @@ class _LikedTab extends ConsumerWidget {
   }
 }
 
+/// Skeleton→content cross-fade duration. Matches home_screen so the
+/// reveal feel is consistent across surfaces. See _tileRevealDuration
+/// in home_screen.dart for the rationale.
+const Duration _likedTileReveal = Duration(milliseconds: 220);
+
 /// Liked-Artists carousel tile. Skeleton until artistTileProvider
 /// yields a populated row.
 class _LikedArtistTile extends ConsumerWidget {
@@ -640,10 +645,17 @@ class _LikedArtistTile extends ConsumerWidget {
   @override
   Widget build(BuildContext context, WidgetRef ref) {
     final artist = ref.watch(artistTileProvider(id)).asData?.value;
-    if (artist == null) return const SkeletonArtistTile();
-    return ArtistCard(
-      artist: artist,
-      onTap: () => context.push('/artists/${artist.id}', extra: artist),
+    return AnimatedSwitcher(
+      duration: _likedTileReveal,
+      switchInCurve: Curves.easeOut,
+      child: artist == null
+          ? const SkeletonArtistTile(key: ValueKey('skeleton'))
+          : ArtistCard(
+              key: ValueKey('artist-${artist.id}'),
+              artist: artist,
+              onTap: () =>
+                  context.push('/artists/${artist.id}', extra: artist),
+            ),
     );
   }
 }
@@ -657,10 +669,16 @@ class _LikedAlbumTile extends ConsumerWidget {
   @override
   Widget build(BuildContext context, WidgetRef ref) {
     final album = ref.watch(albumTileProvider(id)).asData?.value;
-    if (album == null) return const SkeletonAlbumTile();
-    return AlbumCard(
-      album: album,
-      onTap: () => context.push('/albums/${album.id}', extra: album),
+    return AnimatedSwitcher(
+      duration: _likedTileReveal,
+      switchInCurve: Curves.easeOut,
+      child: album == null
+          ? const SkeletonAlbumTile(key: ValueKey('skeleton'))
+          : AlbumCard(
+              key: ValueKey('album-${album.id}'),
+              album: album,
+              onTap: () => context.push('/albums/${album.id}', extra: album),
+            ),
     );
   }
 }
@@ -677,21 +695,27 @@ class _LikedTrackRow extends ConsumerWidget {
   @override
   Widget build(BuildContext context, WidgetRef ref) {
     final track = ref.watch(trackTileProvider(id)).asData?.value;
-    if (track == null) return const SkeletonTrackRow();
-    return TrackRow(
-      track: track,
-      onTap: () {
-        final hydrated = <TrackRef>[];
-        for (final i in sectionIds) {
-          final v = ref.read(trackTileProvider(i)).asData?.value;
-          if (v != null) hydrated.add(v);
-        }
-        final start = hydrated.indexWhere((t) => t.id == id);
-        ref.read(playerActionsProvider).playTracks(
-              hydrated,
-              initialIndex: start < 0 ? 0 : start,
-            );
-      },
+    return AnimatedSwitcher(
+      duration: _likedTileReveal,
+      switchInCurve: Curves.easeOut,
+      child: track == null
+          ? const SkeletonTrackRow(key: ValueKey('skeleton'))
+          : TrackRow(
+              key: ValueKey('track-${track.id}'),
+              track: track,
+              onTap: () {
+                final hydrated = <TrackRef>[];
+                for (final i in sectionIds) {
+                  final v = ref.read(trackTileProvider(i)).asData?.value;
+                  if (v != null) hydrated.add(v);
+                }
+                final start = hydrated.indexWhere((t) => t.id == id);
+                ref.read(playerActionsProvider).playTracks(
+                      hydrated,
+                      initialIndex: start < 0 ? 0 : start,
+                    );
+              },
+            ),
     );
   }
 }