test(flutter): re-enable drift tests after ci-flutter:1.26 ships libsqlite3-0

Drops the libsqlite3-missing skip cohort now that the ci-flutter
runner image installs libsqlite3-0 (CI-runner commit on its main).

Per-file removals (no behavior change in tests themselves — they
just stop being skipped):
- `@Tags(['drift'])` + `library;` directive from 5 files.
- `const _skipDrift = ...;` declaration + its rationale comment
  from 6 files (the 5 above + like_button_test.dart, which had its
  own _skipDrift for the rollback-via-drift case).
- `skip: _skipDrift` annotations from 17 test invocations across
  those 6 files (16 single-line + 1 multi-line in like_button).
- Stale `@Tags(['drift']) tier covers it` reference in
  home_screen_test.dart's drift-coverage comment.

Net -79 +18 lines across 7 files; 17 previously-silent tests are
now part of the CI signal. Fable #399.

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

flutter_client/test/likes/like_button_test.dart

@@ -43,14 +43,8 @@ class _ThrowingLikesApi implements LikesApi {
       const Paged<ArtistRef>(items: [], total: 0, limit: 50, offset: 0);
 }
 
-// libsqlite3 missing on flutter-ci runner; the rollback assertion now
-// depends on drift writes via LikesController. Re-enable when the runner
-// image carries libsqlite3-dev (Fable #399).
-const _skipDrift = true;
-
 void main() {
-  testWidgets('tap toggles icon optimistically; rollback on error',
-      skip: _skipDrift, (tester) async {
+  testWidgets('tap toggles icon optimistically; rollback on error', (tester) async {
     final api = _ThrowingLikesApi();
     final container = ProviderContainer(overrides: [
       likesApiProvider.overrideWith((ref) async => api),