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/src/components/Header.tsx

@@ -1,13 +1,14 @@
-import type { User } from 'oidc-client-ts';
+import type { AuthUser } from '@/auth/types';
 import { Button } from './ui/button';
 import { Separator } from './ui/separator';
 import { LogOut, Home, Filter } from 'lucide-react';
 import { logout } from '@/auth/authService';
+import { clearPasskeyUser } from '@/auth/passkeyService';
 import { HealthIndicator } from './HealthIndicator';
 import { TaskIndicator } from './TaskIndicator';
 
 interface HeaderProps {
-    user: User;
+    user: AuthUser;
     activeFilterCount?: number;
     taskID?: string | null;
     isLoading?: boolean;
@@ -24,6 +25,15 @@ export function Header({
     showFilterToggle = false,
     onTaskCancelled,
 }: HeaderProps) {
+    const handleLogout = async () => {
+        if (user.provider === 'passkey') {
+            clearPasskeyUser();
+            window.location.reload();
+        } else {
+            await logout();
+        }
+    };
+
     return (
         <header className="flex h-14 shrink-0 items-center gap-3 border-b bg-background px-4">
             {/* Logo / Brand */}
@@ -63,12 +73,12 @@ export function Header({
             {/* User Menu */}
             <div className="flex items-center gap-3">
                 <span className="text-sm text-muted-foreground hidden md:inline">
-                    {user.profile.email}
+                    {user.email}
                 </span>
                 <Button
                     variant="ghost"
                     size="sm"
-                    onClick={logout}
+                    onClick={handleLogout}
                     className="gap-2"
                 >
                     <LogOut className="h-4 w-4" />