[REQUEST] hammer-editor

### Package name

hammer-editor

### Current version

N/A

### New version

3.8.1

### Upstream source

https://github.com/Darkrock-Studios/hammer-editor/releases

### Reason for request

Neat book editor that apparently [doesn't match the requirements to be published on FlatHub](https://www.reddit.com/r/fossdroid/comments/1v9ag2u/comment/p0dkxmq/) (also comes as an AppImage, I guess)

### Additional context

*No response*

Start by reviewing the repository's existing package definitions and the hammer-editor 3.8.1 release at the linked upstream source. Follow the local packaging pattern and verify that the package metadata points to version 3.8.1 and builds successfully.

Written by the indexing model from the issue text.