feat(auth): passkey enrolment, login button + admin settings UI

PasskeysSection in account settings (add/rename/remove with a current-password step-up), a 'Sign in with a passkey' button on the login page, the admin enable + RP-ID/origins controls, and a per-user admin reset action.

client/src/components/Settings/AccountTab.tsx

@@ -8,6 +8,7 @@ import { authApi, adminApi } from '../../api/client'
 import { getApiErrorMessage } from '../../types'
 import type { UserWithOidc } from '../../types'
 import Section from './Section'
+import PasskeysSection from './PasskeysSection'
 
 const MFA_BACKUP_SESSION_KEY = 'trek_mfa_backup_codes_pending'
 
@@ -395,6 +396,9 @@ export default function AccountTab(): React.ReactElement {
           </div>
         </div>
 
+        {/* Passkeys */}
+        <PasskeysSection demoMode={demoMode} />
+
         {/* Avatar */}
         <div className="flex items-center gap-4">
           <div style={{ position: 'relative', flexShrink: 0 }}>