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/library/library_providers.dart

@@ -1,5 +1,4 @@
 import 'dart:async';
-import 'dart:convert';
 
 import 'package:dio/dio.dart';
 import 'package:drift/drift.dart' as drift;
@@ -16,7 +15,6 @@ import '../cache/connectivity_provider.dart';
 import '../cache/db.dart';
 import '../models/album.dart';
 import '../models/artist.dart';
-import '../models/home_data.dart';
 import '../models/home_index.dart';
 import '../models/track.dart';
 
@@ -44,57 +42,6 @@ final libraryApiProvider = FutureProvider<LibraryApi>((ref) async {
   return LibraryApi(await ref.watch(dioProvider.future));
 });
 
-/// Drift-first home data (#357 follow-up). The home screen is the first
-/// view the user sees on app open; without a local cache the cold-start
-/// blocks on the /api/home round-trip, which is the dominant felt-
-/// latency on slow / remote connections.
-///
-/// Cache layout: a single row in `cached_home_snapshot` storing the
-/// last successful HomeData as JSON. On stream subscription:
-///
-///   - If a row exists, yield it immediately (parsed from JSON) and
-///     kick off a background revalidation against /api/home (SWR).
-///     The drift watch() re-emits when the new row is written.
-///   - If no row exists yet (cold cache), fetch /api/home synchronously,
-///     upsert into drift, and emit. Subsequent emissions come from the
-///     drift watch as background revalidations land.
-///
-/// The HomeData JSON encodes back to the same wire shape /api/home
-/// emits, so the existing HomeData.fromJson handles both sources.
-final homeProvider = StreamProvider<HomeData>((ref) {
-  final db = ref.watch(appDbProvider);
-  return cacheFirst<CachedHomeSnapshotData, HomeData>(
-    driftStream: db.select(db.cachedHomeSnapshot).watch(),
-    fetchAndPopulate: () async {
-      final api = await ref.read(libraryApiProvider.future);
-      final fresh = await api.getHome();
-      await db.into(db.cachedHomeSnapshot).insertOnConflictUpdate(
-            CachedHomeSnapshotCompanion.insert(
-              json: _encodeHomeData(fresh),
-              updatedAt: drift.Value(DateTime.now()),
-            ),
-          );
-    },
-    toResult: (rows) => rows.isEmpty
-        ? const HomeData(
-            recentlyAddedAlbums: [],
-            rediscoverAlbums: [],
-            rediscoverArtists: [],
-            mostPlayedTracks: [],
-            lastPlayedArtists: [],
-          )
-        : HomeData.fromJson(jsonDecode(rows.first.json) as Map<String, dynamic>),
-    isOnline: () async => (await ref
-        .read(connectivityProvider.future)
-        .timeout(const Duration(seconds: 3), onTimeout: () => true)),
-    // SWR: when cached snapshot exists, still hit /api/home in the
-    // background so the user sees the freshest curation. The cache
-    // mostly serves the first frame, not the canonical state.
-    alwaysRefresh: true,
-    tag: 'home',
-  );
-});
-
 /// Drift-first per-item home index. Reads from cached_home_index
 /// (populated by /api/home/index discovery) and yields a HomeIndex
 /// the screen consumes to lay out section→tile slots. Each tile is
@@ -184,49 +131,6 @@ final homeIndexProvider = StreamProvider<HomeIndex>((ref) {
   );
 });
 
-/// Encodes HomeData back to the wire-format JSON shape /api/home
-/// emits, so HomeData.fromJson can round-trip through the drift cache.
-String _encodeHomeData(HomeData h) => jsonEncode({
-      'recently_added_albums': h.recentlyAddedAlbums.map(_albumToJson).toList(),
-      'rediscover_albums': h.rediscoverAlbums.map(_albumToJson).toList(),
-      'rediscover_artists': h.rediscoverArtists.map(_artistToJson).toList(),
-      'most_played_tracks': h.mostPlayedTracks.map(_trackToJson).toList(),
-      'last_played_artists': h.lastPlayedArtists.map(_artistToJson).toList(),
-    });
-
-Map<String, dynamic> _albumToJson(AlbumRef a) => {
-      'id': a.id,
-      'title': a.title,
-      'sort_title': a.sortTitle,
-      'artist_id': a.artistId,
-      'artist_name': a.artistName,
-      'year': a.year,
-      'track_count': a.trackCount,
-      'duration_sec': a.durationSec,
-      'cover_url': a.coverUrl,
-    };
-
-Map<String, dynamic> _artistToJson(ArtistRef a) => {
-      'id': a.id,
-      'name': a.name,
-      'sort_name': a.sortName,
-      'album_count': a.albumCount,
-      'cover_url': a.coverUrl,
-    };
-
-Map<String, dynamic> _trackToJson(TrackRef t) => {
-      'id': t.id,
-      'title': t.title,
-      'album_id': t.albumId,
-      'album_title': t.albumTitle,
-      'artist_id': t.artistId,
-      'artist_name': t.artistName,
-      'track_number': t.trackNumber,
-      'disc_number': t.discNumber,
-      'duration_sec': t.durationSec,
-      'stream_url': t.streamUrl,
-    };
-
 /// Drift-first per #357 plan C. Watches cached_artists for the row;
 /// when empty + online, fetches via REST + populates drift, which
 /// re-emits via watch().