- Add Home/Profile links to nav bar alongside Vault/Settings/Logout
- Profile page: change email, display name, password
- TOTP 2FA: setup with QR code, verify, disable with password
- Login flow: two-step TOTP challenge when 2FA is enabled
- Backend: new endpoints PUT /profile, POST /totp/setup|verify|disable
- Migration: add totp_secret and totp_enabled columns to users
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>