Add ChatGPT Prompt extension to contrib

[GravityPoet]

Summary

Adds a new extension at contrib/ChatGPTPrompt.popclipext.

This extension keeps direct send behavior for ChatGPT while adding a dialog step to collect a follow-up question before sending.

What it does

1. User selects text.
2. PopClip action opens a question dialog.
3. Extension composes:

【原文】
<selected text>

【问题】
<follow-up question>

4. Opens https://chatgpt.com/?q=... to send through ChatGPT's URL flow.

Advantages vs existing ChatGPT Website extension

Compared with 73pbck (ChatGPT Website), this extension adds:

• Inline follow-up question dialog before sending.
• Structured prompt format for better context clarity.
• Same direct-send URL path (q) for simple no-clipboard workflow.

Included files

• Config.json
• chatgpt.applescript
• Readme.md

Manual test

• Verified popup dialog behavior.
• Verified URL encoding and ChatGPT URL opening.
• Verified AppleScript compiles on macOS.

[GravityPoet]

Hi maintainer, friendly ping for review when you have time. I have validated the extension behavior locally and can update promptly if any changes are required. Thank you!

[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.