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/library/home_screen_test.dart

@@ -12,8 +12,7 @@ import 'package:minstrel/playlists/playlists_provider.dart';
 import 'package:minstrel/theme/theme_data.dart';
 
 // All tests pump an empty HomeIndex unless they care about populated
-// section IDs — per-tile hydration is intentionally not exercised here
-// (that requires drift, and the @Tags(['drift']) tier covers it).
+// section IDs — per-tile hydration is intentionally not exercised here.
 // What this suite verifies is the screen's section-level shape:
 // placeholders / empty-state copy / section presence given the index.
 const _emptyIndex = HomeIndex.empty;