feat: add skill validation CI job

[CybotTM]

Summary

• Add skill validation job calling reusable workflow from skill-repo-skill
• Checks SKILL.md frontmatter, word count, composer.json, plugin.json, file presence

Test plan

• CI passes with new validation job

[gemini-code-assist]

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[Copilot]

Pull request overview

This PR adds a new CI job to validate skill repository structure and content by calling a reusable workflow from the netresearch/skill-repo-skill repository. The validation checks SKILL.md frontmatter, word count, composer.json, plugin.json, and file presence to ensure the repository meets skill standards.

Changes:

• Added validate job to lint.yml workflow that calls a reusable workflow for skill validation

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[Copilot]

The reusable workflow reference uses @main which is a mutable branch reference. All other action references in this repository use pinned commit SHAs for security (e.g., @de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2). Using @main allows the referenced workflow to change without your knowledge, potentially introducing malicious code or breaking changes. Consider pinning to a specific commit SHA or at minimum a tagged version, following the established pattern in this codebase.

Suggested change

	uses: netresearch/skill-repo-skill/.github/workflows/validate.yml@main
	uses: netresearch/skill-repo-skill/.github/workflows/validate.yml@v1

[Copilot]

The validate job does not explicitly define permissions. When calling a reusable workflow, permissions are not inherited by default from the caller workflow. If the reusable workflow needs to access repository contents or other resources, you may need to explicitly pass permissions using the 'permissions' key at the job level, or ensure the reusable workflow has 'permissions: read-all' or specific permissions defined. Verify whether the netresearch/skill-repo-skill validate.yml workflow requires any specific permissions.

Suggested change

	name: Skill Validation
	name: Skill Validation
	permissions:
	contents: read