chore: align quality gate with credo strict

[mikehostetler]

Summary

• align mix quality with credo --strict and keep README/CONTRIBUTING consistent with the real quality gate
• clean up strict Credo findings across core modules and tests so the documented bar is actually true
• remove noisy OpenAI Responses unit-test warnings by using the request :id field when checking deep-research tooling

Validation

• mix test
• mix quality