Backup Migration <= 2.1.5.1 - Authenticated (Administrator+) OS Command Injection via 'file' Parameter

The Backup Migration plugin for WordPress is vulnerable to OS Command Injection in all versions up to, and including, 2.1.5.1 due to insufficient sanitization of the `file` POST parameter on the `restoreBackup()` AJAX handler. The handler applies `esc_attr()` — an HTML-context sanitizer that does not strip shell metacharacters — and concatenates the result, unquoted, into a `php-cli -f … bmi_restore <file> <remote>` command passed to `exec()`. This makes it possible for authenticated attackers, with Administrator-level access (or any user granted the plugin's `do_backups` capability) and above, to execute arbitrary OS commands as the web-server user, bypassing WordPress hardening constants such as `DISALLOW_FILE_EDIT` and `DISALLOW_FILE_MODS` that would otherwise prevent code execution from the admin UI. This is an incomplete fix of CVE-2023-7002, which patched the same pattern only in the `$_POST['url']` path of `handleQuickMigration()`; the equivalent mitigations (`rawurlencode()` + explicit shell-metachar replacement + double-quoting in `exec()`) were never applied to `$backupName`.