Add PopScript extension

[FurtherSecrets24680]

PopScript

Convert selected text into Unicode subscript or superscript with one click.

What it does

• ₓ: Converts numbers to subscript. Example: C6H12O6 -> C₆H₁₂O₆.
• ˣ: Converts numbers to superscript. Example: x2 + y10 -> x² + y¹⁰.

Settings

• Convert + - = ( ) symbols too: Also converts supported symbols to sub/sup variants.
• Also convert text (default: off): Converts letters where Unicode subscript/superscript forms exist.

More

• Supports full-width digits (０-９) by normalizing them first.
• Handles full-width symbols (＋－＝（）) when symbol conversion is enabled.
• Normalizes minus variants (− – —) for consistent symbol conversion.

[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.