Add an admin-controlled `require_mfa` policy in App Settings and expose it via `/auth/app-config` so the client can enforce it globally. Users without MFA are redirected to Settings after login and blocked from protected API/WebSocket access until setup is completed, while preserving MFA setup endpoints and admin recovery paths. Also prevent enabling the policy unless the acting admin already has MFA enabled, and block MFA disable while the policy is active. Includes UI toggle in Admin > Settings, required-policy notice in Settings, client-side 403 `MFA_REQUIRED` handling, and i18n updates for all supported locales.
- Demo user gets 403 on all upload endpoints (files, photos, cover, avatar)
- Admin uploads still work normally
- PDF export back in modal popup using srcdoc iframe
- Zero behavior change when DEMO_MODE is not set
fgbona