Enhance document upload in DA

DA has improved image uploads, but document handling still requires authors to use the DAM (Digital Asset Manager) for uploads and publishing. It would be amazing if this could be streamlined.

The ideal workflow would allow:
- Drag-and-drop document uploads directly in DA
- Automatic publishing with a shareable URL returned to the user
- No DAM dependency for basic document linking

This would simplify content creation, matching the convenience already offered for images.

Start by tracing the existing image-upload workflow in DA and compare it with the current DAM-based document flow. Define the scope for drag-and-drop uploads, automatic publishing, and returning a shareable URL; done means basic document linking works without a DAM dependency.

Written by the indexing model from the issue text.