[bug]: Missing Attachment Upload Space

### what happened?

As usual, I posted a devlog with the attachment being <50 MB (the limit, of course). However, after editing the devlog and replacing the attachment with one >50 MB, due to the upper limit, this strips the devlog of any attachment. This creates a devlog with no attachment nor the ability to add one.

### what did you expect to happen?

There should be a drop zone to rectify the missing attachment while editing the devlog. Deleting the devlog in this case would be another fix, but this causes a 500 error.

### how do we make it happen?

1. post a devlog
2. edit the devlog and replace the attachment with one that is larger than 50 MB
3. save your changes and there's now a devlog with no attachment

### show us!

### where were you?

/projects page, chrome, windows 11

Start on the projects page in Chrome on Windows 11 and reproduce the edit flow: replace an attachment with one over 50 MB, then save. Trace the devlog attachment validation and edit state; done means the oversized replacement cannot leave the devlog without an attachment or a way to add one, and deleting the affected devlog no longer causes a 500 error.

Written by the indexing model from the issue text.