Track failures via body island, not accumulating comments

Replaces the per-run add-comment approach on #37864 with a bounded list maintained inside a gh-aw replace-island in the issue body.

- safe-outputs: drop add-comment; scope update-issue to target 37864 with body updates enabled and max:1.

- Known Pre-existing Failures section: parse the tracking island, fetch each linked issue's state, drop entries whose issue is closed (no re-open logic; recurring failures get a fresh issue and a new entry).

- Step 6 rewritten to emit one update_issue call per run with operation: replace-island and the reconciled list as body. The framework owns the island markers (gh-aw-island-start:fix-test-failures / gh-aw-island-end:fix-test-failures).

- Lock file regenerated via gh aw compile (incidentally bumps the github/gh-aw-actions/setup pin from v0.72.1 to v0.77.5 because that is the gh-aw version installed locally).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jeremymeng