docs: enable private vulnerability reporting

[solnikhil]

Summary

• enable GitHub private vulnerability reporting for the repository
• link SECURITY.md directly to the private advisory submission form
• explicitly keep exploit and reproduction details out of public issues

Verification

• GitHub API reports private vulnerability reporting as enabled
• git diff --check

Closes #18

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[coderabbitai]

Important

• 🔍 Trigger review

This repository does not receive automatic reviews because it has fewer than 10 stars.

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 74971dbf-6ab7-4d45-8eac-98552e8f80b7

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}