Add passkey (WebAuthn) authentication with self-registration

Enable users to sign up and sign in using passkeys (biometrics/security
keys) without needing a manually-created Authentik account. The existing
SSO login remains as an alternative.

Backend:
- Add WebAuthn registration/authentication endpoints via py-webauthn
- Issue HS256 JWTs for passkey users, with Redis-backed challenge storage
- Dual JWT verification in auth middleware (issuer-based routing: passkey
  HS256 vs Authentik RS256)
- PasskeyCredential model + migration making user.password nullable
- UserRepository with full CRUD for users and credentials

Frontend:
- AuthUser type abstraction unifying OIDC and passkey users
- Passkey service using @simplewebauthn/browser for WebAuthn ceremonies
- LoginModal redesigned with Sign In / Sign Up tabs
- Type migration from oidc-client-ts User to AuthUser across all services
  and components

crawler/frontend/package.json

@@ -24,7 +24,9 @@
     "@radix-ui/react-separator": "^1.1.7",
     "@radix-ui/react-slider": "^1.3.6",
     "@radix-ui/react-slot": "^1.2.3",
+    "@radix-ui/react-tabs": "^1.1.13",
     "@radix-ui/react-tooltip": "^1.2.7",
+    "@simplewebauthn/browser": "^10.0.0",
     "@tabler/icons-react": "^3.34.0",
     "@tailwindcss/vite": "^4.1.10",
     "@types/crossfilter": "^0.0.38",