feat: integrate Logto OIDC for user authentication

- Add Logto OIDC integration (app/core/logto.py): CookieStorage adapter,
  create/decode session token helpers, sync_logto_user upsert
- New auth endpoints (/api/v1/auth): sign-in, callback, sign-out, me
- AuthRedirectMiddleware: protects HTML pages, redirects to /setup when
  Logto is unconfigured, to /login otherwise
- Update require_admin_auth: accepts dmarq_session cookie JWT first,
  then API key, then Bearer JWT (fully backward compatible)
- Update User model: add logto_id, username, picture, created_at, updated_at;
  make hashed_password nullable for Logto-only users; is_superuser default=True
- New Alembic migration d4e5f6a7b8c9 for the above schema changes
- Add LOGTO_ENDPOINT / LOGTO_APP_ID / LOGTO_APP_SECRET / LOGTO_REDIRECT_URI
  settings with logto_configured property
- Create login.html (Sign in with Logto button) and setup.html (step-by-step
  configuration guide)
- Update base.html: user menu with avatar/name and sign-out via Alpine.js
  fetch to /api/v1/auth/me
- Update settings.html: remove localStorage adminApiKey; session cookie is
  sent automatically by browser; add 401 → /login redirect
- Update requirements.txt: replace fastapi-users additions with logto + aiohttp
- Add test_auth.py: 18 new tests covering session tokens, CookieStorage,
  sync_logto_user, /me, /sign-in (503), /sign-out cookie clearing
- Fix test_security_extra.py: pass Request mock to require_admin_auth;
  add new test_valid_session_cookie_returns_auth_context

Agent-Logs-Url: https://github.com/christianlouis/dmarq/sessions/b448f585-7646-40f8-ae2d-9986c361e3fd

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

backend/app/tests/test_stats_endpoints.py

@@ -89,18 +89,14 @@ class TestDomainStatistics:
         response = client.get("/api/v1/stats/domain/example.com?force_refresh=true")
         assert response.status_code == 200
 
-    def test_domain_stats_force_refresh_calls_invalidate_with_domain(
-        self, client: TestClient
-    ):
+    def test_domain_stats_force_refresh_calls_invalidate_with_domain(self, client: TestClient):
         """Verify invalidate_cache is called with the domain ID."""
         with patch("app.api.api_v1.endpoints.stats.StatsSummarizer") as MockSummarizer:
             mock_instance = MagicMock()
             mock_instance.calculate_summary_statistics.return_value = {"total": 0}
             MockSummarizer.return_value = mock_instance
 
-            response = client.get(
-                "/api/v1/stats/domain/example.com?force_refresh=true"
-            )
+            response = client.get("/api/v1/stats/domain/example.com?force_refresh=true")
             assert response.status_code == 200
             mock_instance.invalidate_cache.assert_called_once_with("example.com")