Add SlideJot PopClip extension

[Hawstein]

Hi Nick @pilotmoon ,

I've created an extension for my macOS app, SlideJot (https://slidejot.com/). It allows users to send selected text directly to a new Jot in the app.

• Source: contrib/SlideJot.popclipext
• Icon: Included a 256x256 PNG icon as requested
• Testing: Tested and working on PopClip (latest version) and macOS 26.2

Thanks for reviewing!

[pilotmoon]

Thanks for the pull request, and sorry for the slow reply — you may have noticed the pace of adoption of new extensions has been slow. That's because maintaining a large repo containing hundreds of extensions has become too onerous.

To solve the problem I've built a new way to submit extensions to the PopClip Extensions Directory. It is now ready, and I encourage you to use it instead.

Extensions are no longer added to this repository. Instead, you'll keep your extension in your own public repo, and the directory will pull it in whenever you push a version tag. You keep control of the code, you get your own author page in the directory, and each submission gets automatic feedback via GitHub.

Here's how to set it up: 👉 Submit an Extension 👈

I'll close this PR soon to keep things tidy. I hope you'll send it through the new way, and thanks for contributing.