refactor: remove ccw-chain phases, add @commands/ resolver, ccw chain-loader CLI, workflow-skill command

- Delete all 60+ duplicate phase files under .claude/skills/ccw-chain/phases/
- Update chain JSON content_ref to point to @commands/ or @skills/ sources
- Add @commands/ prefix support in resolveFileRef and resolveInlineRefs
- Add `ccw chain-loader [json]` CLI command as thin wrapper
- Add /workflow-skill command for direct skill invocation by name
- Move chain-based workflow skills to .claude/workflow-skills/

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

Author: catlog22