File stays AES-GCM encrypted with a fixed app-internal key — opaque
without the app, which is the only protection we actually need for
locally-stored API keys. Removes the modal and both password dialogs.
AES-256-GCM + PBKDF2 encrypted config backup (.mhu files).
Export/import all accounts, settings, and history.
Pre-import safety backup of current config.
Password modal with confirmation for export.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>