新增自动代码评审 Agent 示例

[douzhenyu]

概述

新增 skills_code_review_agent 示例，实现一个基于 Skill、沙箱执行、Filter 治理、SQLite 落库和结构化报告的自动代码评审 Agent 原型。

Closes #92

主要变更

• 新增 code-review Skill、规则文档和检查脚本。
• 新增 diff 解析、沙箱执行、去重降噪、脱敏、落库和报告生成链路。
• 新增 9 个测试 fixture，包括真实 sandbox runtime failure 场景。
• 新增 README、架构说明和阶段规格文档。

修改类型

• 新功能
• 示例工程
• 测试补充
• 文档补充

测试覆盖

• clean/security/async/db/tests/dedup/sandbox/sensitive fixtures
• Filter 拦截与 denied script 不执行
• 沙箱失败降级与 DB/report 记录
• 敏感信息脱敏与 dry-run 链路

自测清单

• test_cr_agent.py 23 tests passed
• 真实 failure fixture 可运行
• 未提交 .env、.tmp_*、SQLite DB 等运行产物

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

@@            Coverage Diff             @@
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  Coverage        ?   87.51874%           
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  Files           ?         467           
  Lines           ?       44018           
  Branches        ?           0           
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  Hits            ?       38524           
  Misses          ?        5494           
  Partials        ?           0           

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[douzhenyu]

I have read the CLA Document and I hereby sign the CLA