Allow users to permanently delete account from the UI

Acceptance Criteria: Users must be able to permanently delete their account and all their files through the UI. This should include a warming and an "accept" button to prevent accidental deletion. Confirmation email should also be sent for users with email.

No files, tests, or entry points are named. Start by locating the account settings UI and the existing account and file deletion flows; verify how users with and without email are handled. Done means the UI requires a warning and acceptance action, permanently removes the account and all files, and sends a confirmation email when applicable.

Written by the indexing model from the issue text.