009: Triage Agent Only Triggers on issues.opened

Problem

The triage agent workflow only triggers on issues: types: [opened]. If triage fails (workflow bug, transient error, API timeout), there is no way to re-trigger it on the same issue without creating a duplicate.

Observed

Triage agent failed on Issue #8 due to invalid github_issue_number input. After the workflow fix was merged, the issue could not be re-triaged.

Proposed Fix

Add reopened to the trigger:

on:
  issues:
    types: [opened, reopened]

Maintainers can close and reopen an issue to re-trigger triage. The triage logic is idempotent (uses in-place comment updates), so re-running is safe.