[Phase 4.2] GitHub integration: link existing issues to feedback

[Andreas-Froyland]

Goal

Let org admins manually link an existing GitHub issue to a Veerify feedback item. Useful when work has already started on GitHub before the feedback was created in Veerify.

Depends on: #16 (create issues from feedback) - builds on the same linking system

Flow

1. Org admin is on a feedback detail page ([Phase 2.3] Build feedback detail view #13)
2. Clicks "Link GitHub issue"
3. A search modal appears:
   • Text input to search issues in the linked repo
   • Calls GitHub Issues API with the query
   • Shows results: issue number, title, status
4. Admin selects an issue
5. Link is saved in github_issue_links
6. Feedback detail now shows the linked issue

Notes

• Only one GitHub issue can be linked per feedback item (for MVP)
• Can unlink later (remove the link, doesn't delete the GitHub issue)
• Search is scoped to the project's linked repo only

Why this matters

• Sometimes issues are created on GitHub first, then feedback comes in
• Manually linking them keeps everything connected
• Users can see the GitHub issue status from Veerify