feat: Convert to Claude Code plugin marketplace

Transform repository into a plugin marketplace structure with two plugins:

- claude-code plugin: Complete toolkit with 5 skills
  * claude-code-plugins
  * claude-code-slash-commands
  * claude-code-hooks
  * claude-code-subagents
  * claude-code-memory

- claude-skills plugin: Meta-skill for creating Agent Skills
  * Comprehensive best practices guide
  * Templates and examples
  * Progressive disclosure patterns

Infrastructure:
- Add marketplace.json manifest
- Create plugin.json for each plugin
- Update documentation for marketplace structure
- Add contribution and testing guides

Installation:
- /plugin install claude-code@claude-skills
- /plugin install claude-skills@claude-skills

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.gitignore

@@ -1 +1,58 @@
+# Claude Code local settings
 .claude/settings.local.json
+
+# macOS
+.DS_Store
+.AppleDouble
+.LSOverride
+
+# Temporary files
+*.tmp
+*.swp
+*.swo
+*~
+.*.sw?
+
+# Test artifacts
+tmp/
+temp/
+test-output/
+
+# Compressed skill packages
+*.zip
+*.tar.gz
+
+# IDE
+.vscode/
+.idea/
+*.sublime-*
+
+# Python (if testing skills)
+__pycache__/
+*.py[cod]
+*$py.class
+.pytest_cache/
+.coverage
+htmlcov/
+.venv/
+venv/
+ENV/
+
+# Node (if testing skills)
+node_modules/
+npm-debug.log
+yarn-error.log
+.npm/
+
+# Build outputs
+dist/
+build/
+*.egg-info/
+
+# Sensitive data
+*.key
+*.pem
+*.cert
+secrets/
+.env
+.env.local