feat: MFA frontend with auth page restyling, challenge screen, and setup wizard

- Restyle organizer auth pages: Dutch text, remove placeholder social login
- Restyle portal auth pages to Vuexy v1 centered card pattern with decorative shapes
- MFA challenge card component with VOtpInput, method tabs, backup code input,
  trusted device checkbox, and session countdown timer
- Login pages handle mfa_required response with device fingerprint header
- Security settings page with TOTP setup (QR code), email setup, disable MFA,
  backup codes regeneration, and trusted devices management
- Portal profile page includes MFA security section
- Admin user detail page shows MFA status with reset button
- MFA enforcement route guard redirects to security settings when required
- Device fingerprint utility for trusted device identification
- MFA types, composables with TanStack Query for both apps

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/app/components.d.ts

@@ -70,6 +70,10 @@ declare module 'vue' {
     ImportFromEventDialog: typeof import('./src/components/event/ImportFromEventDialog.vue')['default']
     InfoTooltip: typeof import('./src/components/common/InfoTooltip.vue')['default']
     InviteMemberDialog: typeof import('./src/components/members/InviteMemberDialog.vue')['default']
+    MfaChallengeCard: typeof import('./src/components/auth/MfaChallengeCard.vue')['default']
+    MfaDisableDialog: typeof import('./src/components/settings/MfaDisableDialog.vue')['default']
+    MfaEmailSetupDialog: typeof import('./src/components/settings/MfaEmailSetupDialog.vue')['default']
+    MfaTotpSetupDialog: typeof import('./src/components/settings/MfaTotpSetupDialog.vue')['default']
     MoreBtn: typeof import('./src/@core/components/MoreBtn.vue')['default']
     Notifications: typeof import('./src/@core/components/Notifications.vue')['default']
     OrganisationSwitcher: typeof import('./src/components/layout/OrganisationSwitcher.vue')['default']