feat(flutter): SWR everywhere + nav hydration + cold-start home skeleton

Three changes addressing the cold-start spinner + stale-on-revisit pain.

A. SWR on remaining cacheFirst providers
- artistProvider, artistAlbumsProvider, artistTracksProvider all gain
  alwaysRefresh: true. Cache hit still renders instantly; one
  background refresh per subscription keeps the row from going stale
  forever.
- albumProvider (inline async*) and playlistDetailProvider (inline
  async*) now keep a `revalidated` flag and kick a one-shot
  background fetch on the first complete cache hit. Same effect as
  cacheFirst's alwaysRefresh, just inline.
- Three providers gained the connectivity timeout that
  album/artist/playlist already had.

B. Navigation hydration
- AlbumDetailScreen accepts `AlbumRef? seed`; ArtistDetailScreen
  accepts `ArtistRef? seed`. When the live provider is still loading,
  the seed populates cover/title/artist immediately so the page
  isn't blank.
- Routing wires `extra: AlbumRef|ArtistRef` from go_router into
  the seed parameter.
- Call sites updated: home (Recently added, Rediscover albums +
  artists, Last played), artist detail album grid. Where a ref isn't
  available (track actions sheet), the screen falls back to the
  spinner — no regression.

C. Cold-start home skeleton
- Replace the full-screen CircularProgressIndicator on /home with a
  layout-preserving skeleton: 5 section titles + 6 grey card-shaped
  placeholders per row. The page feels populated immediately;
  sections fill in independently as data arrives via the per-section
  providers.
- Drops the unused DelayedLoading import.

Net effect: re-visits to detail screens render instantly (cache hit
+ silent refresh); first visit from a tile shows the seed header
immediately while tracks load; cold-start home shows a layout
skeleton instead of a 30s blank spinner.

flutter_client/lib/library/artist_detail_screen.dart

@@ -12,22 +12,49 @@ import 'library_providers.dart';
 import 'widgets/album_card.dart';
 
 class ArtistDetailScreen extends ConsumerWidget {
-  const ArtistDetailScreen({required this.id, super.key});
+  const ArtistDetailScreen({required this.id, this.seed, super.key});
   final String id;
 
+  /// Optional artist reference from the caller. Lets the screen render
+  /// the name + avatar immediately while albums load.
+  final ArtistRef? seed;
+
   @override
   Widget build(BuildContext context, WidgetRef ref) {
     final fs = Theme.of(context).extension<FabledSwordTheme>()!;
     final artist = ref.watch(artistProvider(id));
     final albums = ref.watch(artistAlbumsProvider(id));
 
+    // Resolve which artist info to render in the header. Live wins
+    // when present and populated; seed fills the gap during the
+    // first frame after navigation.
+    final liveArtist = artist.value;
+    final hasLiveName = liveArtist != null && liveArtist.name.isNotEmpty;
+    final effective = hasLiveName ? liveArtist : (seed ?? liveArtist);
+
     return Scaffold(
       appBar: AppBar(),
       backgroundColor: fs.obsidian,
       body: artist.when(
         error: (e, _) => Center(child: Text('$e', style: TextStyle(color: fs.error))),
-        loading: () => const Center(child: CircularProgressIndicator()),
-        data: (a) => ListView(children: [
+        // While loading: render header from seed if available so the
+        // page isn't blank.
+        loading: () => seed == null
+            ? const Center(child: CircularProgressIndicator())
+            : _artistBody(context, ref, seed!, albums, fs),
+        data: (_) => _artistBody(context, ref, effective ?? seed!, albums, fs),
+      ),
+    );
+  }
+
+  Widget _artistBody(
+    BuildContext context,
+    WidgetRef ref,
+    ArtistRef a,
+    AsyncValue<List<AlbumRef>> albums,
+    FabledSwordTheme fs,
+  ) =>
+      ListView(children: [
           Padding(
             padding: const EdgeInsets.all(16),
             child: Row(children: [
@@ -111,16 +138,14 @@ class ArtistDetailScreen extends ConsumerWidget {
                     width: cellW,
                     titleMaxLines: 2,
                     showArtist: false,
-                    onTap: () => context.push('/albums/${album.id}'),
+                    onTap: () =>
+                        context.push('/albums/${album.id}', extra: album),
                   );
                 },
               );
             }),
           ),
-        ]),
-      ),
-    );
-  }
+        ]);
 }
 
 /// Renders the artist's avatar. Server-emitted coverUrl wins when