Adds two new sections to the tenant Settings page:
- MfaSection: TOTP authenticator setup with QR code, 6-digit verification,
backup code display (2-column grid with copy/download), and MFA removal
- MfaEnforcementToggle: tenant admin control to require MFA for all members,
with confirmation dialog before enabling
Installs qrcode.react for QR code rendering. Uses existing MFA hooks from
tenant-hooks.ts and design-system components.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>