Polish docs and harden webhook verification

[scottsgeorge]

Summary

• Rewrite repository and sample READMEs for clear setup and usage guidance
• Harden webhook signature verification by requiring a secret and normalizing payloads
• Clean up webhook server import formatting

Testing

• node --check javascript/webhooks-node/server.mjs
• node --check javascript/webhooks-express/verify-signature.mjs

---

Codex Task

[chatgpt-codex-connector]

You have reached your Codex usage limits for code reviews. You can see your limits in the Codex usage dashboard.
To continue using code reviews, you can upgrade your account or add credits to your account and enable them for code reviews in your settings.