[Feature] Publish GitHub Action for CI/CD integration

[rohitg00]

Problem

No official GitHub Action for skillkit. Users can't easily:

• Install skills in CI/CD pipelines
• Cache skill installs between runs
• Validate skill configs are in sync
• Run security scans as PR checks

Proposed Solution

Publish rohitg00/skillkit-action GitHub Action:

- uses: rohitg00/skillkit-action@v1
  with:
    command: install
    source: anthropics/skills
    agents: claude-code,cursor
    cache: true

Features

• install — install skills with caching
• sync — sync skills to agents, fail if out of sync
• scan — security scan as PR check
• validate — validate skill format
• Skill caching via actions/cache (keyed on source + lockfile hash)
• --check mode: fail if config is out of sync (for drift detection)

Outputs

• installed-skills — JSON list of installed skills
• scan-results — JSON security scan results
• cache-hit — whether cache was used

Acceptance Criteria

• Action published to GitHub Marketplace
• Caching reduces install time by >80% on cache hit
• Example workflow in README