feat: add AI brand representation snapshot - #21

Summary

• add the versioned ai-brand-representation-snapshot@1.0.0 recipe and its three controlled channel capabilities
• add the closed ai-brand-representation-snapshot/v1 result contract with provider-neutral framing, observation, comparison, and cost structures
• enforce exact channel coverage, preflight all-stop behavior, outcome-driven state, multi-row comparison evidence, observed-time coupling, and arithmetic cost reconciliation
• update installed skill routing, method boundaries, contract guidance, behavioral scenarios, fixtures, documentation, and release metadata for v0.5.0

Verification

• npm run validate — 7 recipes, 5 result contracts, 70 contract fixtures, and 40 registered behavioral cases
• fresh-context execution of all nine issue-specific behavioral scenarios — pass; affected failure scenario rerun on the final candidate — pass
• npm run release:preflight -- v0.5.0 — pass with byte-identical two-build assets
  • release tree: 5a5b36083f404e793a4a72f6d5b06dc9c3d45516e91aa4eaec926898ff9a602b
  • checksums: 2567d0b5adae566634d7ea2e4910e53c4e939885e5b825b4125b77f63c0f787b
• three fresh read-only candidate reviews covering methodology, schema/fixtures, and delivery/disclosure — pass on b8133e4d6c5fd3275ace867249bdaecfac93017d

Closes #15