feat: implement skills system

[JeremyDev87]

implement skills system

📋 Summary

This PR implements a cross-platform skills system that allows AI assistants to access reusable workflows and best practices. Skills are stored as YAML frontmatter + Markdown files and can be accessed via MCP tools (list_skills, get_skill). The implementation includes comprehensive validation, security checks, and initial skill library.

🎯 Reason for Change

The skills system enables consistent development practices across different AI assistants (Claude Code, Codex, Cursor). By providing reusable workflows as structured skills, we can:

• Standardize development practices
• Enable AI assistants to follow proven workflows
• Reduce repetitive instructions in prompts
• Create a library of reusable best practices

🔧 Key Changes

1. Skill Schema and Validation

• Implemented Zod-based schema validation for skill files
• YAML frontmatter parsing with required fields (name, description)
• Prototype pollution prevention (shared utility)
• Content validation (non-empty after frontmatter)

2. MCP Tools

• list_skills: Returns all available skills with name and description
• get_skill: Retrieves full skill content by name
• Input validation and error handling
• Path traversal protection

3. Initial Skill Library

Added 9 core skills:

• test-driven-development: Red-Green-Refactor cycle guidance
• systematic-debugging: Root cause investigation process
• writing-plans: Implementation plan creation
• executing-plans: Plan execution workflow
• subagent-driven-development: Subagent dispatch patterns
• dispatching-parallel-agents: Parallel agent coordination
• brainstorming: Brainstorming techniques
• frontend-design: Frontend design workflow

4. Code Organization

• Extracted containsDangerousKeys to shared security utils (used by both agent and skill schemas)
• Refactored agent schema to use shared security utility
• Comprehensive test coverage for all new functionality

5. Documentation

• Skills README with usage guide
• Adapter documentation updates (claude-code, codex, cursor)
• Implementation plan document

⚠️ Breaking Changes

None

📌 Migration Guide

No migration needed. This is a new feature addition.

✅ Testing

All changes include comprehensive test coverage:

• Skill schema validation tests (valid/invalid cases, security)
• Skill loading tests (list, get, error cases)
• MCP tool integration tests
• Path traversal protection tests

Run tests:

yarn test

📦 Changed Files

Core Implementation:

• apps/mcp-server/src/rules/skill.schema.ts - Skill schema and validation
• apps/mcp-server/src/rules/skill.schema.spec.ts - Schema tests
• apps/mcp-server/src/mcp/mcp-serverless.ts - Skill loading and MCP tools
• apps/mcp-server/src/mcp/mcp-serverless.spec.ts - Integration tests
• apps/mcp-server/src/shared/security.utils.ts - Shared security utilities

Skills:

• packages/rules/.ai-rules/skills/README.md - Skills catalog
• packages/rules/.ai-rules/skills/*/SKILL.md - 9 skill files

Documentation:

• packages/rules/.ai-rules/adapters/*.md - Adapter updates
• docs/skills-implementation-plan.md - Implementation plan

Dependencies:

• apps/mcp-server/package.json - Added yaml package
• yarn.lock - Dependency lock file

Total: 21 files changed, 2717 insertions(+), 48 deletions(-)

🔍 Review Checklist

• Skill schema validation implemented and tested
• MCP tools registered and functional
• Path traversal protection applied
• Prototype pollution prevention implemented
• Comprehensive test coverage added
• Initial skill library created
• Documentation updated
• Review skill file format and validation rules
• Verify MCP tool integration works correctly
• Check that skills are accessible via MCP tools

🔗 Related Issues

Closes #116