feat(server): auth comptes utilisateurs et tokens API (ticket #48)

Ajoute la couche application (ports, use cases), les entités du
domaine, l'endpoint api/auth_api.dart (register/login/logout) et son
câblage dans le router, le hashing de mot de passe et le service de
token (infrastructure/security), et l'adapter Postgres des repositories
d'auth s'appuyant sur la table users du ticket #49. dart pub get OK,
dart analyze clean, dart test 10/10 vert (test PostgreSQL réel skip
faute de Docker disponible dans ce sandbox). Logique d'auth et
middleware testés via repositories fake en mémoire ; les endpoints
HTTP register/login/logout n'ont pas pu être exercés de bout en bout
faute d'accès à un vrai PostgreSQL local.

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

server/lib/application/use_cases.dart

@@ -0,0 +1,190 @@
+import '../domain/domain.dart';
+import 'ports.dart';
+
+const _minimumPasswordLength = 8;
+final _emailPattern = RegExp(r'^[^@\s]+@[^@\s]+\.[^@\s]+$');
+
+final class RegisterUserUseCase {
+  const RegisterUserUseCase({
+    required this.users,
+    required this.passwordHasher,
+    required this.clock,
+    required this.ids,
+  });
+
+  final UserRepository users;
+  final PasswordHasher passwordHasher;
+  final Clock clock;
+  final IdGenerator ids;
+
+  Future<UserAccount> execute({
+    required String email,
+    required String password,
+    String? displayName,
+  }) async {
+    final normalizedEmail = _validateEmail(email);
+    _validatePassword(password);
+
+    final existing = await users.findByEmail(normalizedEmail);
+    if (existing != null) {
+      throw const EmailAlreadyTakenException();
+    }
+
+    final now = clock.now().toUtc();
+    final user = UserAccount(
+      id: ids.newId(),
+      email: normalizedEmail,
+      passwordHash: await passwordHasher.hash(password),
+      displayName: _blankToNull(displayName),
+      createdAt: now,
+      updatedAt: now,
+    );
+    await users.insert(user);
+    return user;
+  }
+}
+
+final class LoginResult {
+  const LoginResult({
+    required this.user,
+    required this.session,
+    required this.token,
+  });
+
+  final UserAccount user;
+  final AuthSession session;
+  final String token;
+
+  DateTime get expiresAt => session.expiresAt;
+}
+
+final class LoginUseCase {
+  const LoginUseCase({
+    required this.users,
+    required this.sessions,
+    required this.passwordHasher,
+    required this.tokens,
+    required this.clock,
+    required this.ids,
+    this.sessionDuration = const Duration(days: 30),
+  });
+
+  final UserRepository users;
+  final AuthSessionRepository sessions;
+  final PasswordHasher passwordHasher;
+  final OpaqueTokenService tokens;
+  final Clock clock;
+  final IdGenerator ids;
+  final Duration sessionDuration;
+
+  Future<LoginResult> execute({
+    required String email,
+    required String password,
+    String? userAgent,
+    String? deviceLabel,
+  }) async {
+    final normalizedEmail = _validateEmail(email);
+    final user = await users.findByEmail(normalizedEmail);
+    if (user == null || user.isDisabled) {
+      throw const InvalidCredentialsException();
+    }
+    final verified = await passwordHasher.verify(
+      password: password,
+      passwordHash: user.passwordHash,
+    );
+    if (!verified) {
+      throw const InvalidCredentialsException();
+    }
+
+    final now = clock.now().toUtc();
+    final token = tokens.generateToken();
+    final session = AuthSession(
+      id: ids.newId(),
+      userId: user.id,
+      tokenHash: tokens.hashToken(token),
+      issuedAt: now,
+      expiresAt: now.add(sessionDuration),
+      userAgent: _blankToNull(userAgent),
+      deviceLabel: _blankToNull(deviceLabel),
+    );
+    await sessions.insert(session);
+    return LoginResult(user: user, session: session, token: token);
+  }
+}
+
+final class LogoutUseCase {
+  const LogoutUseCase({
+    required this.sessions,
+    required this.tokens,
+    required this.clock,
+  });
+
+  final AuthSessionRepository sessions;
+  final OpaqueTokenService tokens;
+  final Clock clock;
+
+  Future<void> execute({required String token}) async {
+    final session = await sessions.findByTokenHash(tokens.hashToken(token));
+    if (session == null || !session.isActiveAt(clock.now())) {
+      throw const UnauthorizedException();
+    }
+    await sessions.revoke(
+      sessionId: session.id,
+      revokedAt: clock.now().toUtc(),
+    );
+  }
+}
+
+final class AuthenticatedRequest {
+  const AuthenticatedRequest({required this.user, required this.session});
+
+  final UserAccount user;
+  final AuthSession session;
+}
+
+final class AuthenticateRequestUseCase {
+  const AuthenticateRequestUseCase({
+    required this.users,
+    required this.sessions,
+    required this.tokens,
+    required this.clock,
+  });
+
+  final UserRepository users;
+  final AuthSessionRepository sessions;
+  final OpaqueTokenService tokens;
+  final Clock clock;
+
+  Future<AuthenticatedRequest> execute({required String token}) async {
+    final session = await sessions.findByTokenHash(tokens.hashToken(token));
+    if (session == null || !session.isActiveAt(clock.now())) {
+      throw const UnauthorizedException();
+    }
+    final user = await users.findById(session.userId);
+    if (user == null || user.isDisabled) {
+      throw const UnauthorizedException();
+    }
+    return AuthenticatedRequest(user: user, session: session);
+  }
+}
+
+String _validateEmail(String email) {
+  final normalized = email.trim().toLowerCase();
+  if (!_emailPattern.hasMatch(normalized)) {
+    throw const ValidationException('Email format is invalid.');
+  }
+  return normalized;
+}
+
+void _validatePassword(String password) {
+  if (password.length < _minimumPasswordLength) {
+    throw const ValidationException(
+      'Password must contain at least 8 characters.',
+    );
+  }
+}
+
+String? _blankToNull(String? value) {
+  final trimmed = value?.trim();
+  return trimmed == null || trimmed.isEmpty ? null : trimmed;
+}