Add Claude Plugins Marketplace (2389 Research)

[sophiealula]

Summary

• Adds a curated marketplace of 25+ open-source Claude Code plugins and MCP servers from 2389 Research
• Includes claude-plugins-marketplace/SKILL.md with full documentation and README entry in Development & Code Tools

What's in the marketplace

The claude-plugins registry covers testing, code review, development workflows, and business tools. Highlights:

• simmer — iterative artifact refinement with subagent judge feedback
• test-kitchen — parallel exploration of implementation approaches
• fresh-eyes-review — pre-commit/PR sanity checks
• review-squad — multi-agent code review from multiple perspectives (experts, normies, nitpickers)
• prbuddy — PR health monitoring and CI triage
• Plus 20+ more plugins and 4 MCP servers

All plugins are open-source, individually installable, and production-tested.

Test plan

• SKILL.md follows the template format (YAML frontmatter with name/description, sections for When to Use, What This Skill Does, How to Use, Examples, Tips)
• README.md entry added alphabetically in Development & Code Tools section
• All linked repos are public and accessible