chore: update fullsend shim workflow

[fullsend-ai-fullsend]

This PR updates the fullsend shim workflow to match the current template in the .fullsend config repo.

The shim content has drifted from the template — this brings it back in sync.

[fullsend-ai-retro]

🤖 Finished Retro · ✅ Success · Started 7:24 PM UTC · Completed 7:28 PM UTC
Commit: 7d4aece · View workflow run →

[fullsend-ai-retro]

Retro: PR #5 — chore: update fullsend shim workflow

Workflow: Bot-generated onboarding PR with a single-line change (runs-on: ubuntu-latest → runs-on: ubuntu-24.04). No review agent, code agent, or fix agent ran. Merged by a human after ~10 hours with no formal reviews.

Finding: This retro run itself is the main inefficiency — it consumed tokens analyzing a trivial bot-generated PR with zero agent interaction. There is nothing meaningful to retroanalyze.

No new proposals. The relevant improvements are already tracked by existing open issues in fullsend-ai/fullsend:

• #2739 — Skip retro dispatch for merged bot PRs with no agent interaction (directly applies here)
• #2638 — Skip retro dispatch for merged bot PRs with no review findings
• #1371 — Skip review dispatch for bot-authored PRs
• #2639 / #2842 — Fast-path or cheaper review for trivial bot-authored PRs

Recommendation: prioritize #2739 to eliminate wasteful retro runs on bot onboarding PRs.