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!