docs(skills): update SKILL.md format documentation to match implementation

[Ceheps]

Summary

Fix Skills guide documentation to match actual SDK implementation. Updates both English and Chinese versions of docs/*/guides/skills.md.

Changes:

• Replaced HTML comment format (<!-- skill: ... -->) with YAML frontmatter (---\nname: ...\ndescription: ...\n---) in SKILL.md examples
• Removed metadata.json from directory structure (code never reads this file)
• Added field reference table documenting required YAML frontmatter fields (name, description)
• Added note clarifying name field behavior differences between SkillsManager (uses folder name) and SkillsManagementManager (requires frontmatter name)

Closes #52

Motivation / Context

The current documentation describes SKILL.md format as HTML comments and lists metadata.json as optional metadata. However, actual code implementation requires YAML frontmatter and never reads metadata.json. This discrepancy causes confusion for developers following the documentation, resulting in skills being silently skipped during loading.

Type of Change

• Bug fix
• Feature
• Refactor
• Docs
• Test
• Chore / Build

Scope / Modules

• core (agent / events / pool / room / scheduler)
• infra (db / provider / sandbox / store)
• tools (fs / bash / mcp / skills / task)
• skills
• examples
• docs (en / zh-CN)
• tests
• other: ___

Public API

• Exports changed in src/index.ts
• No public API change

Breaking Changes

• Yes , and attach report(include necessity) and transition plan
• No

Testing

• npm run test:unit(required)
• npm run test:integration(if needed)
• npm run test:e2e(if needed)

Results: 243 passed, 1 failed. The single failure is sqlite-store module load error (EBUSY: resource busy or locked, unlink), which is an environment-level file lock issue on Windows unrelated to this documentation change.

Impact / Risk

Low risk — pure documentation update with no code changes. Aligns documentation with existing behavior rather than changing behavior.

Checklist

• Docs updated if needed
• Examples updated if needed
• New feature includes related tests and docs
• Tests follow tests/README.md structure
• Docs follow docs/en + docs/zh-CN format rules
• No secrets or tokens committed
• No dist/ changes (unless release)
• Only one lockfile updated for the package manager used