v1.14.0

Add 'Export ZIP only' flow & bump version

Introduce a new "Esporta solo ZIP" UI and AJAX flow so users can generate/download the static site ZIP without requiring GitHub credentials or a repository. Changes:

- assets/admin.js: new button handler and UI enable/disable logic for #sed-start-zip.
- includes/class-sed-admin.php: register wp_ajax_sed_start_zip, implement ajax_start_zip, remove the ad-hoc build_plugin_zip admin action and its dashboard link.
- includes/class-sed-queue.php: add start_job($trigger, $force_zip_only) param and force ZIP-only mode when requested; adjust payload flags accordingly.
- readme.txt & static-export-deploy.php: bump plugin version to 1.14.0 and add changelog entry.

This makes it possible to create the static ZIP without triggering deploy validations or needing tokens/repo config.