Add Darklua icon

### Type

- [x] File icon
- [ ] Folder icon

### Context and associations

- `*.darklua.json` to have a Darklua icon

### References

Website: https://darklua.com/

![favicon](https://github.com/user-attachments/assets/9c7f8513-ef3d-4007-aa64-7ee5785ba35b)

If color is required/preferred the website's primary color is `#644b8a`