skill: package expo/skills into dockyard

[JAORMX]

Package agent skills from expo/skills into the Dockyard registry.

Source

• Repo: https://github.com/expo/skills
• License: MIT
• Skill count upstream: ~12
• Trust signal: Official Expo/EAS; 1.8k stars

Candidate skills

Full curation at packaging time.

Acceptance criteria

• One spec.yaml per selected skill under skills/<name>/
• spec.ref pinned to an audited upstream commit SHA
• task validate-skill passes for each
• task scan-skill findings triaged
• Single PR grouping all Expo skills (branch skills/expo)

Part of the vendor-by-vendor sweep following #466 (Trail of Bits).