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/album_detail_screen.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
 import '../api/endpoints/likes.dart';
+import '../models/album.dart';
 import '../cache/audio_cache_manager.dart';
 import '../cache/db.dart';
 import '../likes/like_button.dart';
@@ -12,18 +13,78 @@ import 'library_providers.dart';
 import 'widgets/track_row.dart';
 
 class AlbumDetailScreen extends ConsumerWidget {
-  const AlbumDetailScreen({required this.id, super.key});
+  const AlbumDetailScreen({required this.id, this.seed, super.key});
   final String id;
 
+  /// Optional album reference passed by the caller (typically the
+  /// tile they tapped) so the header can render immediately while
+  /// the full provider loads tracks. Hydration only — provider data
+  /// still wins once it arrives.
+  final AlbumRef? seed;
+
   @override
   Widget build(BuildContext context, WidgetRef ref) {
     final fs = Theme.of(context).extension<FabledSwordTheme>()!;
+    final live = ref.watch(albumProvider(id));
+
+    // Pick the best header info available: live data > seed > nothing.
+    final headerTitle = live.value?.album.title.isNotEmpty == true
+        ? live.value!.album.title
+        : seed?.title ?? '';
+    final headerArtist = live.value?.album.artistName.isNotEmpty == true
+        ? live.value!.album.artistName
+        : seed?.artistName ?? '';
+
+    Widget header() => Padding(
+          padding: const EdgeInsets.all(16),
+          child: Row(children: [
+            ClipRRect(
+              borderRadius: BorderRadius.circular(6),
+              child: SizedBox(
+                width: 96,
+                height: 96,
+                child: ServerImage(
+                  url: '/api/albums/$id/cover',
+                  fit: BoxFit.cover,
+                  fallback: Container(color: fs.slate),
+                ),
+              ),
+            ),
+            const SizedBox(width: 16),
+            Expanded(
+              child: Column(
+                crossAxisAlignment: CrossAxisAlignment.start,
+                children: [
+                  Text(
+                    headerTitle,
+                    style: TextStyle(
+                      color: fs.parchment,
+                      fontFamily: fs.display.fontFamily,
+                      fontSize: 22,
+                    ),
+                  ),
+                  if (headerArtist.isNotEmpty)
+                    Text(headerArtist, style: TextStyle(color: fs.ash)),
+                ],
+              ),
+            ),
+          ]),
+        );
+
     return Scaffold(
       appBar: AppBar(),
       backgroundColor: fs.obsidian,
-      body: ref.watch(albumProvider(id)).when(
+      body: live.when(
             error: (e, _) => Center(child: Text('$e', style: TextStyle(color: fs.error))),
-            loading: () => const Center(child: CircularProgressIndicator()),
+            loading: () => seed != null
+                ? ListView(children: [
+                    header(),
+                    const Padding(
+                      padding: EdgeInsets.symmetric(vertical: 24),
+                      child: Center(child: CircularProgressIndicator()),
+                    ),
+                  ])
+                : const Center(child: CircularProgressIndicator()),
             data: (r) => ListView(children: [
               Padding(
                 padding: const EdgeInsets.all(16),