clean up AGENTS.md, mostly pointing to other docs

- Add docs/common/RUNTIME.md - comprehensive guide for runtime development
    (servers, testing, integration tests, debugging)
- Add docs/common/RECIPE_DEV_DEPLOY.md - build, debug, deploy pattern
- Add DEVELOPMENT.md general coding standards, design principles, and best
    practices (removed recipe-specific deployment content)
- Move packages/patterns/README.md -> docs/common/UI_TESTING.md

Author: ellyxir