Add logrus as the primary logging framework with dependency injection
pattern. All errors now use WithError() for context, and structured
logging uses camelCase field names. Tag runtime service with service
field for better log organization.
- Add logrus dependency
- Update Runtime to accept logger via dependency injection
- Add WithLogger() option for logger configuration
- Log errors with WithError() for context
- Log async function failures with service context
- Document logging practices in AGENTS.md
