refactor(flutter): drop legacy home snapshot path (#406)

The home screen renders solely from the per-item cached_home_index
path (proven on devices for many releases); the legacy snapshot stack
was dead weight.

- library_providers: remove homeProvider + _encodeHomeData +
  _albumToJson/_artistToJson/_trackToJson; drop now-unused dart:convert
  and models/home_data.dart imports
- metadata_prefetcher: re-point off homeIndexProvider/HomeIndex —
  pre-warm artistProvider from the rediscover/last-played artist
  sections (album/track tiles hydrate their own artist on render)
- live_events_dispatcher: homeProvider -> homeIndexProvider so live
  events still refresh the home screen
- db.dart: drop CachedHomeSnapshot (table class + @DriftDatabase
  entry); schemaVersion 10->11; from<3 createTable -> raw
  customStatement so the historical step compiles without the
  generated symbol; from<11 DROP TABLE cached_home_snapshot

No test references the removed symbols. db.g.dart regenerated by CI.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

flutter_client/lib/cache/metadata_prefetcher.dart

@@ -1,7 +1,7 @@
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
 import '../library/library_providers.dart';
-import '../models/home_data.dart';
+import '../models/home_index.dart';
 
 /// Pre-warms the drift cache for likely-tap targets. Conservative on
 /// purpose: only warms artistProvider rows (single row, single round
@@ -10,10 +10,15 @@ import '../models/home_data.dart';
 /// list when missing, and pre-warming N albums fans out N parallel
 /// "fetch tracks" round trips that compete with the user's actual
 /// playback request for bandwidth.
+///
+/// Driven off the per-item home path (homeIndexProvider). Only the
+/// artist-typed sections (rediscover / last-played artists) carry
+/// artist ids directly; album/track tiles hydrate their own artist on
+/// render via the per-item path, so warming those here is unnecessary.
 class MetadataPrefetcher {
   MetadataPrefetcher(this._ref) {
-    _ref.listen<AsyncValue<HomeData>>(homeProvider, (_, next) {
-      next.whenData(_warmHome);
+    _ref.listen<AsyncValue<HomeIndex>>(homeIndexProvider, (_, next) {
+      next.whenData(_warmIndex);
     });
   }
 
@@ -24,7 +29,8 @@ class MetadataPrefetcher {
   /// ids we've already warmed.
   final Set<String> _warmedArtists = {};
 
-  /// Cap per section. Covers what fits on screen without scrolling.
+  /// Cap warmed per emission. Covers what fits on screen without
+  /// scrolling.
   static const _topN = 8;
 
   /// Pre-warm artists. Albums are intentionally not pre-warmed —
@@ -39,24 +45,11 @@ class MetadataPrefetcher {
     }
   }
 
-  void _warmHome(HomeData h) {
-    final artistIds = <String>{};
-    for (final a in h.recentlyAddedAlbums.take(_topN)) {
-      if (a.artistId.isNotEmpty) artistIds.add(a.artistId);
-    }
-    for (final a in h.rediscoverAlbums.take(_topN)) {
-      if (a.artistId.isNotEmpty) artistIds.add(a.artistId);
-    }
-    for (final ar in h.rediscoverArtists.take(_topN)) {
-      if (ar.id.isNotEmpty) artistIds.add(ar.id);
-    }
-    for (final ar in h.lastPlayedArtists.take(_topN)) {
-      if (ar.id.isNotEmpty) artistIds.add(ar.id);
-    }
-    for (final t in h.mostPlayedTracks.take(_topN)) {
-      if (t.artistId.isNotEmpty) artistIds.add(t.artistId);
-    }
-    warmArtists(artistIds);
+  void _warmIndex(HomeIndex h) {
+    warmArtists(<String>{
+      ...h.rediscoverArtists.take(_topN),
+      ...h.lastPlayedArtists.take(_topN),
+    });
   }
 
   /// Discards the return value and any error from a fire-and-forget