feat(flutter): drift-first MyQuarantine

Final slice of the smooth-loading pass. Adds CachedQuarantineMine
(schema 5, columnar so flag/unflag can do row-level mutation) and
rewires MyQuarantineController to read from drift via watch() + SWR
refresh; flag/unflag write drift first and roll back on REST failure.

Public API (.flag / .unflag / .isHidden) unchanged so existing call
sites (library_screen Hidden tab, TrackActionsSheet) keep working.

Tests updated to match: bypassed-build-via-_StubController approach
no longer makes sense now that state lives in drift, so the suite is
rewritten against NativeDatabase.memory() with the same libsqlite3
skip the sync_controller suite uses on the CI runner.

The Hidden tab now paints from disk on cold open, the list is
queryable offline, and a flag from another device that arrived in
this user's quarantine via SSE-triggered invalidate lands the same
way as a local flag.

flutter_client/lib/cache/db.dart

@@ -142,6 +142,29 @@ class CachedHistorySnapshot extends Table {
   Set<Column> get primaryKey => {id};
 }
 
+/// Caller-scoped quarantine ("hidden") rows. Mirrors the wire shape of
+/// /api/quarantine/mine — fully denormalized (track + album + artist
+/// fields inline) because the Hidden tab renders straight from this row
+/// without joining other tables. Columnar (vs JSON blob) so flag/unflag
+/// can do row-level INSERT/DELETE; the drift watch() emission feeds
+/// MyQuarantineController state directly. Schema 5+.
+class CachedQuarantineMine extends Table {
+  TextColumn get trackId => text()();
+  TextColumn get reason => text()();
+  TextColumn get notes => text().nullable()();
+  TextColumn get createdAt => text()();
+  TextColumn get trackTitle => text()();
+  IntColumn get trackDurationMs => integer().withDefault(const Constant(0))();
+  TextColumn get albumId => text()();
+  TextColumn get albumTitle => text()();
+  TextColumn get albumCoverArtPath => text().nullable()();
+  TextColumn get artistId => text()();
+  TextColumn get artistName => text()();
+  DateTimeColumn get fetchedAt => dateTime().withDefault(currentDateAndTime)();
+  @override
+  Set<Column> get primaryKey => {trackId};
+}
+
 enum CacheSource { manual, autoLiked, autoPlaylist, autoPrefetch, incidental }
 
 @DriftDatabase(tables: [
@@ -155,12 +178,13 @@ enum CacheSource { manual, autoLiked, autoPlaylist, autoPrefetch, incidental }
   SyncMetadata,
   CachedHomeSnapshot,
   CachedHistorySnapshot,
+  CachedQuarantineMine,
 ])
 class AppDb extends _$AppDb {
   AppDb([QueryExecutor? e]) : super(e ?? driftDatabase(name: 'minstrel_cache'));
 
   @override
-  int get schemaVersion => 4;
+  int get schemaVersion => 5;
 
   @override
   MigrationStrategy get migration => MigrationStrategy(
@@ -188,6 +212,12 @@ class AppDb extends _$AppDb {
             // empty on upgrade; first /api/me/history fetch populates.
             await m.createTable(cachedHistorySnapshot);
           }
+          if (from < 5) {
+            // Schema 5: cached_quarantine_mine for drift-first Hidden
+            // tab. Empty on upgrade; first /api/quarantine/mine fetch
+            // populates. Optimistic flag/unflag also writes here.
+            await m.createTable(cachedQuarantineMine);
+          }
         },
       );
 }