Mirror2 gold/ajax save-fix overlay

This overlay replaces only UI/backend source files. It preserves config.local.php, the SQLite database, recipients, campaigns, suppressions, queue, cron token, and admin password.

Changed files:
- app.php: stronger recipient add/update persistence, duplicate handling, suppression handling, and worker batch hard cap.
- api.php: adds recipient_add and returns domain in recipient_list.
- index.php: gold public login structure, body classes, recipient add/edit UI.
- assets/app.js: robust JSON handling, visible save states, add-recipient Ajax, improved inline save/delete/suppress.
- assets/style.css: black/gold uploaded theme plus small recipient-management additions.
