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>

lib/infrastructure/local/drift_repositories.dart

@@ -35,6 +35,35 @@ final class DriftExerciseRepository implements ExerciseRepository {
   }
 }
 
+final class DriftMediaAssetRepository implements MediaAssetRepository {
+  const DriftMediaAssetRepository(this.database);
+
+  final db.AppDatabase database;
+
+  @override
+  Future<domain.MediaAsset?> findById(String id) async {
+    final row = await (database.select(
+      database.mediaAssets,
+    )..where((table) => table.id.equals(id))).getSingleOrNull();
+    return row == null ? null : _mediaAssetFromRow(row);
+  }
+
+  @override
+  Future<List<domain.MediaAsset>> listActive() async {
+    final rows = await (database.select(
+      database.mediaAssets,
+    )..where((table) => table.deletedAt.isNull())).get();
+    return rows.map(_mediaAssetFromRow).toList();
+  }
+
+  @override
+  Future<void> save(domain.MediaAsset mediaAsset) async {
+    await database
+        .into(database.mediaAssets)
+        .insertOnConflictUpdate(_mediaAssetCompanion(mediaAsset));
+  }
+}
+
 final class DriftProgramRepository implements ProgramRepository {
   const DriftProgramRepository(this.database);
 
@@ -294,6 +323,49 @@ domain.Exercise _exerciseFromRow(db.Exercise row) {
   );
 }
 
+db.MediaAssetsCompanion _mediaAssetCompanion(domain.MediaAsset asset) {
+  final values = _metadataValues(asset.metadata);
+  return db.MediaAssetsCompanion(
+    id: values[0] as Value<String>,
+    createdAt: values[1] as Value<DateTime>,
+    updatedAt: values[2] as Value<DateTime>,
+    deletedAt: values[3] as Value<DateTime?>,
+    schemaVersion: values[4] as Value<int>,
+    syncState: values[5] as Value<String>,
+    localRevision: values[6] as Value<int>,
+    originDeviceId: values[7] as Value<String>,
+    futureOwnerProfileId: values[8] as Value<String?>,
+    lastSyncedAt: values[9] as Value<DateTime?>,
+    remoteRevision: values[10] as Value<String?>,
+    kind: Value(_mediaKindToDb(asset.kind)),
+    localUri: Value(asset.localUri),
+    mimeType: Value(asset.mimeType),
+    sizeBytes: Value(asset.sizeBytes),
+    width: Value(asset.width),
+    height: Value(asset.height),
+    durationMs: Value(asset.durationMs),
+    checksum: Value(asset.checksum),
+    remoteUri: Value(asset.remoteUri),
+    thumbnailLocalUri: Value(asset.thumbnailLocalUri),
+  );
+}
+
+domain.MediaAsset _mediaAssetFromRow(db.MediaAsset row) {
+  return domain.MediaAsset(
+    metadata: _metadataFromRow(row),
+    kind: _mediaKindFromDb(row.kind),
+    localUri: row.localUri,
+    mimeType: row.mimeType,
+    sizeBytes: row.sizeBytes,
+    width: row.width,
+    height: row.height,
+    durationMs: row.durationMs,
+    checksum: row.checksum,
+    remoteUri: row.remoteUri,
+    thumbnailLocalUri: row.thumbnailLocalUri,
+  );
+}
+
 db.ProgramsCompanion _programCompanion(domain.Program program) {
   final values = _metadataValues(program.metadata);
   return db.ProgramsCompanion(
@@ -741,6 +813,17 @@ String _activeStatusToDb(domain.ActiveWorkoutStatus status) => switch (status) {
   domain.ActiveWorkoutStatus.abandoned => 'abandoned',
 };
 
+String _mediaKindToDb(domain.MediaKind kind) => switch (kind) {
+  domain.MediaKind.image => 'image',
+  domain.MediaKind.video => 'video',
+};
+
+domain.MediaKind _mediaKindFromDb(String value) => switch (value) {
+  'image' => domain.MediaKind.image,
+  'video' => domain.MediaKind.video,
+  _ => throw domain.DomainException('Unknown media kind: $value'),
+};
+
 domain.ActiveWorkoutStatus _activeStatusFromDb(String value) => switch (value) {
   'running' => domain.ActiveWorkoutStatus.running,
   'paused' => domain.ActiveWorkoutStatus.paused,