Summary

This PR updates the reference server config surface and lifecycle handling:

• Adds server-local env config module (openapi/reference-server/config.py)
• Standardizes env prefixes:
  • BOXLITE_SERVER_* for server settings
  • BOXLITE_RUNTIME_* for runtime options used by reference server
• Loads .env from openapi/reference-server/.env by default (or --env-file)
• Adds openapi/reference-server/.env.example (server/runtime only)
• Updates docs for setup, env behavior, and precedence
• Adds strict config parsing tests
• Fixes non-detached lifecycle issue by retaining strong box handles in server memory (ID-keyed cache)

Why

• Clarifies and stabilizes reference-server env contract
• Avoids dependence on legacy env aliases
• Prevents watchdog-triggered shutdown from dropped request-scoped handles

Validation

• python3 -m py_compile on server/config/tests
• python3 -m unittest discover -s openapi/reference-server/tests -p "test_*.py" -v
• Manual create/start/get smoke test confirms start -> running and stable process behavior