Drag-and-drop file upload now works across the entire project page

Before this fix, dragging a file onto the project page in Chrome would navigate away or trigger a browser download. easterbrooka patched the drop handling so files land in the right folder regardless of where on the page they're dropped.

The original drop handlers only covered specific targets: folder rows and the document list container. They also only understood mike's internal MIME types for document and folder drags. Anything coming from the OS - an actual file from Finder or Explorer - fell through to the browser's default behavior, which in Chrome means either navigating to the file or starting a download.

The fix adds a page-level dragover/drop fallback on the outer ProjectPage wrapper that catches OS file drags anywhere on the page and uploads to the project root. Dropping onto a folder row now uploads into that folder rather than only handling internal item moves. Propagation is stopped at the inner layer so the new outer handler doesn't fire twice when an existing handler already caught the event.

On validation, easterbrooka added a client-side suffix check against the set {pdf, docx, doc, txt, eml, xlsx} - the same types the backend accepts. Unsupported files surface an alert naming the offending filenames and listing the accepted types, rather than silently failing or round-tripping to the server to get rejected there.