fix(kiro): 修复 Kiro 智能体格式为 .md + YAML frontmatter

[cloudQuant]

Kiro 自定义子智能体要求 ~/.kiro/agents/.md 格式（带 YAML
frontmatter），而非之前的 .json + prompts/ 分离结构。

修复内容：

• convert.sh/ps1: convert_kiro 直接生成 .md 文件
• install.sh/ps1: install_kiro 复制 .md 文件而非 .json

参考：https://kiro.dev/docs/chat/subagents/

What does this PR do?

Agent Information (if adding/modifying an agent)

• Agent Name:
• Category:
• Specialty:

Checklist

• Follows the agent template structure from CONTRIBUTING.md
• Includes YAML frontmatter with name, description, color
• Has concrete code/template examples (for new agents)
• Tested in real scenarios
• Proofread and formatted correctly