🔒 Enforce HTTPS for OpenAI API requests

[sneakocom]

🎯 What: Added strict validation to ensure call_openai only allows https:// endpoints.
⚠️ Risk: Without this check, sensitive credentials like api_key could potentially be transmitted over unencrypted HTTP, allowing interception by network attackers.
🛡️ Solution: The call_openai function now explicitly raises a ValueError if the provided endpoint does not begin with https://. In addition, cascading identity hashes for subject_adapter.py were updated in preregistration.json, contract.json, verification-report.json, and experiments.json to reflect the new code signature and preserve test correctness.

---

PR created automatically by Jules for task 15064313750557907547 started by @sneakocom

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.