feat(os-skills): add cosh guide skill

[zkl123]

Description

add cosh guide skill

Related Issue

#21

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• [Y] New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional change)
• Performance improvement
• CI/CD or build changes

Scope

• [Y] cosh (copilot-shell)
• agent-sec-core
• os-skills
• agentsight
• Multiple / Project-wide

Checklist

• I have read the Contributing Guide
• My code follows the project's code style
• I have added tests that prove my fix is effective or that my feature works
• I have updated the documentation accordingly
• For cosh: Lint passes, type check passes, and tests pass
• For agent-sec-core (Rust): cargo clippy -- -D warnings and cargo fmt --check pass
• For agent-sec-core (Python): Ruff format and pytest pass
• For os-skills: Skill directory structure is valid and shell scripts pass syntax check
• Lock files are up to date (package-lock.json / Cargo.lock)

Testing

Additional Notes

[CLAassistant]

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[Ziqi002]

1. commit msg should add scope, like "feat(os-skills): add cosh guide skill"
2. Please rebase latest main