Implement GitHub Webhook Integration for Real-Time Event Processing

Community & Support: [LinkedIn Group](https://www.linkedin.com/groups/14656108/) · [Slack #project-nest](https://owasp.slack.com/archives/project-nest)

Active project leaders: Arkadii Yakovets -- [GitHub](https://github.com/arkid15r/) · [LinkedIn](https://www.linkedin.com/in/arkid15r/) · [Slack](https://owasp.slack.com/team/U060W3NKLTF); Kate Golovanova -- [GitHub](https://github.com/kasya/) · [LinkedIn](https://www.linkedin.com/in/kate-golovanova/) · [Slack](https://owasp.slack.com/team/U07PWB1JZ6Z)

[Contributing](https://github.com/owasp/nest/blob/main/CONTRIBUTING.md) · [Code of Conduct](https://github.com/owasp/nest/blob/main/CODE_OF_CONDUCT.md) · [GSoC Mentors](https://github.com/owasp/nest/blob/main/MENTORS.md)

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**Description**
Implement real-time GitHub event ingestion for OWASP Pulse using GitHub webhooks.

The system should process GitHub activity in near real-time and convert incoming events into `ActivityEvent` records for the Pulse feed.

**Webhook events:**

- Pull requests (opened, closed, merged)
- Issues (opened, closed)
- Push events (commits)
- Releases (published)

**Are you going to work on implementing this?**

- [x] Yes
- [ ] No