docs(agents): 补充输出规范

[DCjanus]

Why

• 将推文中的输出规范沉淀到全局 AGENTS 规则中。
• 让“简洁回答”的要求更具体，减少执行时的解释空间。

What

• 在沟通规范下新增“输出规范”小节。
• 补充直接给结论、省略无关背景、按返工成本决定是否追问等规则。

Testing

• 未运行测试；仅更新文档规则。

[coderabbitai]

Important

Review skipped

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Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 5e2512f4-e300-4b89-9127-35a8afc1323c

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Use the checkbox below for a quick retry:

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch docs/agents-output-guidelines

📝 Coding Plan

• Generate coding plan for human review comments

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