skill: package firebase/agent-skills into dockyard

[JAORMX]

Package agent skills from firebase/agent-skills into the Dockyard registry.

Source

• Repo: https://github.com/firebase/agent-skills
• License: Apache-2.0
• Skill count upstream: ~12
• Trust signal: Official Google Firebase; 240 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 Firebase skills (branch skills/firebase)

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