Batches the remaining comment-noise cleanups on top of the activity-log fix:
- Resume comment no longer re-posts the full PR description (## Summary/## Changes) — the PR body and
diff already carry it; the comment just links the PR (the reasoning trail shows what the run did).
- Strip a leading self-header the model sometimes emits ("🤖 **@pm**" on its own line, sometimes
twice) before we prepend our own, so headers aren't doubled.
- Also drop the BEGIN_PR_DESCRIPTION block from the plain reply text, and simplify the activity
block's summary (it repeated "🤖 **@name** — activity log").
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
