feat(media): gestion des médias locaux

Ajoute le stockage local des médias (infrastructure/local/local_media_storage.dart)
et les use cases/ports associés. flutter analyze propre, 7/7 tests
unitaires verts, build APK debug validé.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

test/application/media_use_cases_test.dart

@@ -0,0 +1,188 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:gametime/application/application.dart';
+import 'package:gametime/domain/domain.dart';
+
+void main() {
+  test('imports media and stores sync-ready asset metadata', () async {
+    final mediaRepository = _FakeMediaAssetRepository();
+    final useCase = MediaUseCases(
+      mediaRepository: mediaRepository,
+      exerciseRepository: _FakeExerciseRepository(),
+      storage: _FakeMediaStorage(),
+      clock: _FakeClock(DateTime.utc(2026, 7, 17, 12)),
+      ids: _FakeIds(),
+      originDeviceId: 'device-1',
+    );
+
+    final asset = await useCase.importMedia(
+      sourcePath: '/tmp/source.png',
+      kind: MediaKind.image,
+    );
+
+    expect(asset.kind, MediaKind.image);
+    expect(asset.localUri, 'file:///app/media/id-1.png');
+    expect(asset.mimeType, 'image/png');
+    expect(asset.sizeBytes, 128);
+    expect(asset.width, 10);
+    expect(asset.height, 20);
+    expect(asset.remoteUri, isNull);
+    expect(asset.checksum, isNull);
+    expect(mediaRepository.saved.single.metadata.id, asset.metadata.id);
+  });
+
+  test('attaches imported image to exercise image field', () async {
+    final exerciseRepository = _FakeExerciseRepository()
+      ..exercise = Exercise(
+        metadata: _metadata('exercise-1'),
+        name: 'Squat',
+        hasTimeMeasure: false,
+        hasRepsMeasure: true,
+        hasScoreMeasure: false,
+      );
+    final mediaRepository = _FakeMediaAssetRepository()
+      ..asset = MediaAsset(
+        metadata: _metadata('media-1'),
+        kind: MediaKind.image,
+        localUri: 'file:///app/media/media-1.png',
+      );
+    final useCase = MediaUseCases(
+      mediaRepository: mediaRepository,
+      exerciseRepository: exerciseRepository,
+      storage: _FakeMediaStorage(),
+      clock: _FakeClock(DateTime.utc(2026, 7, 17, 12)),
+      ids: _FakeIds(),
+      originDeviceId: 'device-1',
+    );
+
+    final updated = await useCase.attachToExercise(
+      exerciseId: 'exercise-1',
+      mediaAssetId: 'media-1',
+    );
+
+    expect(updated.imageMediaId, 'media-1');
+    expect(updated.videoMediaId, isNull);
+    expect(exerciseRepository.saved.single.imageMediaId, 'media-1');
+  });
+
+  test('deletes managed files not referenced by active media assets', () async {
+    final storage = _FakeMediaStorage()
+      ..managedUris = {
+        'file:///app/media/kept.png',
+        'file:///app/media/orphan.png',
+      };
+    final mediaRepository = _FakeMediaAssetRepository()
+      ..activeAssets = [
+        MediaAsset(
+          metadata: _metadata('media-1'),
+          kind: MediaKind.image,
+          localUri: 'file:///app/media/kept.png',
+        ),
+      ];
+    final useCase = MediaUseCases(
+      mediaRepository: mediaRepository,
+      exerciseRepository: _FakeExerciseRepository(),
+      storage: storage,
+      clock: _FakeClock(DateTime.utc(2026, 7, 17, 12)),
+      ids: _FakeIds(),
+      originDeviceId: 'device-1',
+    );
+
+    final deletedCount = await useCase.deleteOrphanedManagedFiles();
+
+    expect(deletedCount, 1);
+    expect(storage.deletedUris, ['file:///app/media/orphan.png']);
+  });
+}
+
+EntityMetadata _metadata(String id) {
+  return EntityMetadata(
+    id: id,
+    createdAt: DateTime.utc(2026, 7, 17),
+    updatedAt: DateTime.utc(2026, 7, 17),
+    originDeviceId: 'device-1',
+  );
+}
+
+final class _FakeClock implements Clock {
+  const _FakeClock(this.value);
+
+  final DateTime value;
+
+  @override
+  DateTime now() => value;
+}
+
+final class _FakeIds implements IdGenerator {
+  var _next = 0;
+
+  @override
+  String newId() {
+    _next += 1;
+    return 'id-$_next';
+  }
+}
+
+final class _FakeMediaStorage implements LocalMediaStorage {
+  Set<String> managedUris = const {};
+  final deletedUris = <String>[];
+
+  @override
+  Future<StoredMediaFile> importFile({
+    required String sourcePath,
+    required MediaKind kind,
+    required String stableFileName,
+  }) async {
+    return StoredMediaFile(
+      localUri: 'file:///app/media/$stableFileName.png',
+      mimeType: 'image/png',
+      sizeBytes: 128,
+      width: 10,
+      height: 20,
+    );
+  }
+
+  @override
+  Future<Set<String>> listManagedLocalUris() async => managedUris;
+
+  @override
+  Future<void> deleteByLocalUri(String localUri) async {
+    deletedUris.add(localUri);
+  }
+}
+
+final class _FakeMediaAssetRepository implements MediaAssetRepository {
+  MediaAsset? asset;
+  List<MediaAsset> activeAssets = const [];
+  final saved = <MediaAsset>[];
+
+  @override
+  Future<MediaAsset?> findById(String id) async => asset;
+
+  @override
+  Future<List<MediaAsset>> listActive() async => activeAssets;
+
+  @override
+  Future<void> save(MediaAsset mediaAsset) async {
+    saved.add(mediaAsset);
+    asset = mediaAsset;
+  }
+}
+
+final class _FakeExerciseRepository implements ExerciseRepository {
+  Exercise? exercise;
+  final saved = <Exercise>[];
+
+  @override
+  Future<Exercise?> findById(String id) async => exercise;
+
+  @override
+  Future<List<Exercise>> listActive() async {
+    return exercise == null ? const [] : [exercise!];
+  }
+
+  @override
+  Future<void> save(Exercise exercise) async {
+    saved.add(exercise);
+    this.exercise = exercise;
+  }
+}