feat(skills): add community skill registry with install command

[mvanhorn]

Summary

Add a community skill registry system for discovering and installing skills from Git repositories. This is the foundation of a skill ecosystem, letting the community share, discover, and install skills.

Why this matters

DeerFlow has 17 built-in skills and a well-designed skill system (SKILL.md format, parser, loader, validation, even a skill-creator skill). But there is no way to discover or install community-created skills. The skill-creator can create them, but they have nowhere to go.

Source	Evidence
awesome-openclaw-skills	Curated skill registry with 5,400+ entries
r/LangChain comparison	Agent framework comparisons list skill ecosystems as key differentiator
skill-creator	Creates skills with no distribution path

Changes

• registry.py: fetch_registry(), search_registry(), install_skill_from_repo()
  • Fetches JSON index from a URL (default: this repo's skills/registry.json)
  • Searches by name, description, or tags
  • Clones Git repos, validates SKILL.md frontmatter, copies to skills/community/
  • URL normalization: owner/repo becomes https://github.com/owner/repo.git
• skills/registry.json: Initial index with 5 built-in skill entries
• Makefile: make install-skill URL=https://github.com/user/my-skill

Usage

# Install a community skill from a Git repo
make install-skill URL=https://github.com/user/my-deerflow-skill

# Or from shorthand
make install-skill URL=user/my-deerflow-skill

Installed skills appear in skills/community/ and are loaded alongside public and custom skills.

Testing

3 tests covering search, install, and URL normalization.

This contribution was developed with AI assistance (Codex).