Fix three code bugs

[hdushan]

Fixes insecure HTTP, unencoded URL parameters, and OpenAI client initialization issues.

This PR addresses three bugs:

• Insecure HTTP request: Switched http://httpbun.org/post to https://httpbun.org/post in src/restOperations.js and updated mock tests.
• Unencoded user input: Applied encodeURIComponent to the name parameter in src/restOperations.js's gender function to prevent issues with special characters.
• OpenAI client: Converted src/openAi.js to ESM, added OPENAI_API_KEY validation, and implemented a singleton client instance for efficiency, updating src/openAi.test.js to reflect these changes.

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[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
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