fix: standardize agent/skill YAML frontmatter to Claude Code spec

- Convert 11 .yaml agent files to .md format
- Remove invalid frontmatter fields from 100+ agent files
  (type, color, capabilities, priority, triggers, role, version, etc.)
- Remove malformed hooks fields (Python dict serialization)
- Fix tools field from YAML arrays to comma-separated strings
- Rename 2 lowercase skill.md to SKILL.md
- Remove invalid skill fields (version, tags, category, author, etc.)
- Map invocable -> user-invocable, tools -> allowed-tools in skills

Only valid Claude Code fields remain:
  Agents: name, description, tools
  Skills: name, description, user-invocable, allowed-tools

Co-Authored-By: claude-flow <ruv@ruv.net>