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/requirements.txt

@@ -1,18 +1,13 @@
 fastapi>=0.96.0
 uvicorn>=0.22.0
 sqlalchemy>=2.0.0
-aiosqlite>=0.19.0
-asyncpg>=0.27.0
 pydantic>=2.0.0
 pydantic-settings>=2.0.0
 python-jose[cryptography]>=3.3.0
 passlib[bcrypt]>=1.7.4
 python-multipart>=0.0.6
-fastapi-users[sqlalchemy]>=15.0.0
-fastapi-users-db-sqlalchemy>=7.0.0
-httpx-oauth>=0.14.0
-pyotp>=2.8.0
-qrcode[pil]>=7.4.0
+logto>=0.2.0
+aiohttp>=3.8.0
 alembic>=1.11.0
 pytest>=7.3.1
 pytest-asyncio>=0.21.0