fix(core): link issue to PR via output, clean up PR body

[nerdalytics]

Summary

• Fix issue-PR linking race condition: manage-issue.sh now outputs issue number via GITHUB_OUTPUT, passed to manage-pr.sh as env var instead of re-searching
• Clean up PR body: show a concise update table instead of embedding the full issue report (which included irrelevant "How to Update" instructions)
• Use Closes #N instead of Fixes #N for issue linking

What was wrong

PR 41 was not linked to issue 40 because manage-pr.sh searched for the issue via gh issue list --search seconds after it was created. GitHub's search index hadn't caught up yet, so ISSUE_NUMBER was empty.

Test plan

• Trigger Check Action Versions workflow via workflow_dispatch
• Verify issue number appears in PR body as Closes #N
• Verify PR body has concise table without "How to Update" section