easterbrooka fixes the drag-and-drop trap on project pages

Until this fix, dragging a document from your desktop onto a project page in easterbrooka's fork was a small disaster: miss the narrow strip of the page that had upload wired up, and the browser would either navigate away to the file or start downloading it, kicking you out of your work. The upload zones only existed on folder rows and the document list itself; the header, sidebar gutter, and surrounding padding were all live traps.

The fork now treats the whole project page as a drop target, with files landing in the project root by default or inside a folder if you drop directly on one. There's also a friendly client-side check on file types - PDFs, Word docs, plain text, emails, Excel - that surfaces an alert naming the offending file rather than failing silently or bouncing off the server.