YAML configuration support

[frouaix]

Summary

Allow YAML as an alternative configuration format alongside the existing JSON config.

Details

• Support config.yaml / config.yml at ~/.config/applescript-mcp/ as alternative to config.json
• Define precedence: JSON takes priority if both exist (or make it configurable)
• Add a YAML parsing dependency (e.g., js-yaml)
• Update config loading in packages/mcp-server/src/config/
• Update documentation in README.md

Phase 23 item

From TODO.md

Phase 23: YAML configuration support — Allow YAML as an alternative config format