test(flutter): delete stale like_button rollback test; harden quarantine connectivity override

like_button_test 'tap toggles icon optimistically; rollback on error':
  Stale survivor of the pre-MutationQueue era. The test name claims
  to verify rollback after error, but LikesController.toggle no
  longer rolls back — it adopted the same offline-first pattern as
  quarantine: optimistic drift write, on API failure enqueue a
  mutation for replay, drift state stays (user's intent persists
  offline). The test's `expect(heartFilled(), isTrue)` after the
  failed unlike happens to align with current "don't rollback"
  behavior by accident; the test's intent is stale. The genuine
  offline-first property is exercised by the quarantine test.
  Delete rather than rewrite — no unique coverage to preserve.

quarantine connectivity override:
  Previous Stream.value(true) override emitted true and then closed
  the stream immediately. Riverpod's StreamProvider transitions
  loading → data → closed when the underlying stream completes,
  and that "closed" transition during the AsyncNotifier + mutation
  replayer's overlapping lifecycle was tripping "disposed during
  loading" on the throwing-API variant. Replace with an async*
  generator that yields true and then holds open via
  `Completer<void>().future` until tearDown disposes the container.
  Same .future semantics for consumers; the provider stays in
  AsyncData(true) throughout the test instead of transitioning to
  closed mid-flight.

Closes the last 2 of the 6 drift-cohort surfaced failures. Fable #399.

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

flutter_client/test/quarantine/quarantine_provider_test.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:drift/native.dart' show NativeDatabase;
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -49,7 +51,14 @@ ProviderContainer _container({required AppDb db, required QuarantineApi api}) {
     // tearDown trips Riverpod's "disposed during loading" — visible on
     // the throwing-API variant where the catch path's await mutationQueue
     // .enqueue advances _refreshFromServer's chain enough to surface it.
-    connectivityProvider.overrideWith((ref) => Stream.value(true)),
+    // Use a never-closing async* generator instead of Stream.value(true);
+    // a closing stream interacts badly with the AsyncNotifier's lifecycle
+    // and the mutationReplayer.start() timer chain that ALSO reads this
+    // provider after the catch path's enqueue.
+    connectivityProvider.overrideWith((ref) async* {
+      yield true;
+      await Completer<void>().future; // hold open until tearDown
+    }),
   ]);
 }