feat(online): session compte, stockage sécurisé et adapter API (ticket #64)

Ajoute l'adapter API distant (infrastructure/remote/auth_api.dart,
http_api_client.dart) et le stockage sécurisé du token d'auth
(infrastructure/security/secure_storage_auth_token_store.dart), câblés
dans app_bootstrap.dart. Étend le modèle Drift (migration
schemaVersion 9→10) et la couche application (ports, use cases,
entités) pour la session de compte. flutter pub get OK (ajout http,
flutter_secure_storage), build_runner OK, dart format appliqué,
analyze propre (mêmes infos préexistantes), 109/109 tests verts,
build APK debug validé. Premier ticket du chantier "Ajouter les
features serveur au client" (#63).

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

lib/infrastructure/local/drift_repositories.dart

@@ -140,6 +140,34 @@ final class DriftMediaAssetRepository implements MediaAssetRepository {
   }
 }
 
+final class DriftOnlineAccountRepository implements OnlineAccountRepository {
+  const DriftOnlineAccountRepository(this.database);
+
+  final db.AppDatabase database;
+
+  @override
+  Future<domain.UserAccountSession?> currentSession() async {
+    final row =
+        await (database.select(database.onlineAccountSessions)
+              ..orderBy([(table) => OrderingTerm.desc(table.updatedAt)])
+              ..limit(1))
+            .getSingleOrNull();
+    return row == null ? null : _userAccountSessionFromRow(row);
+  }
+
+  @override
+  Future<void> saveSession(domain.UserAccountSession session) async {
+    await database
+        .into(database.onlineAccountSessions)
+        .insertOnConflictUpdate(_userAccountSessionCompanion(session));
+  }
+
+  @override
+  Future<void> clearSession() async {
+    await database.delete(database.onlineAccountSessions).go();
+  }
+}
+
 final class DriftProgramRepository implements ProgramRepository {
   const DriftProgramRepository(this.database);
 
@@ -1471,6 +1499,38 @@ domain.MediaAsset _mediaAssetFromRow(db.MediaAsset row) {
   );
 }
 
+db.OnlineAccountSessionsCompanion _userAccountSessionCompanion(
+  domain.UserAccountSession session,
+) {
+  return db.OnlineAccountSessionsCompanion(
+    id: Value(session.id),
+    serverUserId: Value(session.serverUserId),
+    email: Value(session.email),
+    displayName: Value<String?>(session.displayName),
+    isLoggedIn: Value(session.isLoggedIn),
+    createdAt: Value(session.createdAt.toUtc()),
+    updatedAt: Value(session.updatedAt.toUtc()),
+    lastAuthenticatedAt: Value<DateTime?>(
+      _utcOrNull(session.lastAuthenticatedAt),
+    ),
+  );
+}
+
+domain.UserAccountSession _userAccountSessionFromRow(
+  db.OnlineAccountSession row,
+) {
+  return domain.UserAccountSession(
+    id: row.id,
+    serverUserId: row.serverUserId,
+    email: row.email,
+    displayName: row.displayName,
+    isLoggedIn: row.isLoggedIn,
+    createdAt: _utc(row.createdAt),
+    updatedAt: _utc(row.updatedAt),
+    lastAuthenticatedAt: _utcOrNull(row.lastAuthenticatedAt),
+  );
+}
+
 db.ProgramsCompanion _programCompanion(domain.Program program) {
   final values = _metadataValues(program.metadata);
   return db.ProgramsCompanion(
@@ -1931,8 +1991,7 @@ _activeExerciseStepProgressStateCompanion(
   );
 }
 
-domain.ActiveExerciseStepProgressState
-_activeExerciseStepProgressStateFromRow(
+domain.ActiveExerciseStepProgressState _activeExerciseStepProgressStateFromRow(
   db.ActiveExerciseStepProgressState row,
 ) {
   return domain.ActiveExerciseStepProgressState(