Address security review feedback from jbtronics:
- Add IS_AUTHENTICATED_FULLY to all sensitive endpoints (create/delete
backup, delete log, download backup, start update, restore)
- Change backup download from GET to POST with CSRF token
- Require password confirmation before downloading backups (backups
contain sensitive data like password hashes and secrets)
- Add DISABLE_BACKUP_DOWNLOAD env var (default: disabled) to control
whether backup downloads are allowed
- Add password confirmation modal with security warning in template
- Add comprehensive tests: auth checks, env var blocking, POST-only
enforcement, status/progress endpoint auth
Add happy-path tests for backup creation, deletion, download,
and log deletion with valid CSRF tokens. Also test the locked
state blocking backup creation.
