(agent): Factory self-improvement audit automation

## Component

Workflows

## Describe the feature

Ship a reference **`coding/factory-audit-v1`** (or scheduled workflow) that periodically reviews recent task trajectories, prompt versions, and automation outcomes—proposing harness improvements (rules, standards, workflow YAML) as issues or draft PRs.

## Use case

Operators running mature background-agent fleets often want an **automation auditor** that reviews prompts and run logs to suggest harness improvements. ABCA has evaluation roadmap items but no packaged **closed-loop self-improvement** workflow operators can enable.

## Proposed solution

1. Scheduled trigger (roadmap) or manual `bgagent submit --workflow factory-audit-v1`.
2. Read-only access to `TaskEvents`, traces, merge outcomes for repo/time window.
3. Output: markdown report artifact in S3 + optional GitHub issue creation.
4. Human approves before any harness file auto-PR.

## Other information

- Complements **Evaluation pipeline**, **LLM-assisted trace analysis**, **A/B prompt experiments**.
- Repo-less or read-only repo mode acceptable.

## Acknowledgements

- [ ] I may be able to implement this feature
- [ ] This might be a breaking change

## Acceptance criteria

- [ ] Reference workflow YAML and prompt shipped under `agent/workflows/`.
- [ ] Produces structured report with actionable recommendations.
- [ ] Does not auto-merge harness changes without HITL.
- [ ] Tests with fixture task history.

agent/workflows/ 配下の既存の workflow と、手動のエントリポイント bgagent submit --workflow factory-audit-v1 から始め、TaskEvents、trace、merge outcome がどのように公開されているかを確認します。完了条件は、参照用の workflow YAML と prompt によって構造化された Markdown レポートが生成され、fixture のタスク履歴がカバーされ、harness の変更を merge する前に HITL が必須になることです。

索引モデルが issue の本文から書いたものです。