feat: add OpenAPI spec transformer Claude Code skill

Add a fully autonomous Claude Code skill that transforms Swagger 2.0
API specs from source repositories into OpenAPI 3.0.0 format for the
documentation site. The skill runs end-to-end without human review
between steps — the human validates locally after completion.

Includes:
- SKILL.md: 8-step autonomous workflow (fetch, transform, diff, test, build)
- references/examples.md: Before/after transformation examples with enums
- references/tag-mapping.md: Path-to-tag mapping rules for gRPC and Staking API
- references/servers.md: Server endpoint reference for all environments
- .gitignore: Track .claude/skills/ but exclude settings.local.json

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: web3jenks