docs: update skill list front matter response

[jay666mnj]

What is the purpose of the change

Update Skill Registry documentation for alibaba/nacos#15345.

The Nacos Skill list response now includes frontMatter parsed from the display version's SKILL.md, so the documentation should describe this response field for users and console/API consumers.

Brief changelog

• Document that Skill list response items include frontMatter.
• Explain that frontMatter is parsed from the display version's SKILL.md YAML front matter.
• Update both Chinese and English Skill Registry docs.

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