lawyered0 locks folder deletion to project owners

As things stand, the delete path apparently treats everyone with access to a shared project the same, so any member can remove a folder, not just the person who owns the project. lawyered0's change adds an ownership check: only the project owner gets to delete a folder.

The fix also handles the knock-on effect. Deleting a folder takes the documents nested inside it too, so the same restriction has to cover the contents, not only the top-level folder. lawyered0 flags this directly, which suggests the guard protects the whole tree of documents underneath rather than a single button. This is squarely an access-control tightening in the project and document management layer; the substance is the permission logic itself, and it is still an open proposal on the upstream project.