Module issue_router 

Root issue routing for GitHub events.

Maps GitHub events (issues, PRs, comments, CI checks) back to their root issue for correct Orchestrator session routing.

Three routing strategies:

1. Direct: issues.* events use issue.number directly
2. Ref parsing: Comment/PR bodies contain ref #N (injected by gh wrapper)
3. PR map: check_run events use PR number → root issue lookup

Structs

IssueRouter

Maps PR numbers to root issue numbers.