MDW Admin Documents v3 Polish + Preview

Upload this patch over your existing site/admin files.

Files changed:
- devworks-admin/assets/admin.css
- devworks-admin/lib/document-render.php
- devworks-admin/document-edit.php
- devworks-admin/document-view.php
- devworks-admin/document-preview.php

Changes:
- Adds Preview in New Tab from the document edit screen.
- Adds Pop-out Preview from the document view screen.
- Improves form field readability in MDW Admin.
- Improves document table readability with light rows and dark text.
- Updates document letterhead to use the current MDW logo image when available.
- Keeps existing save/export/email flow intact.

No ECT, vsadmin, database, public storefront, ClearChat, or updater files are changed.
