Integrate compiler warning features into `reference_integration`

### What

Confirm that the warning features can be consumed correctly in a representative downstream integration.

### Acceptance Criteria (DoD)

- `reference_integration` consumes the new compiler warning features from `score_cpp_policies`.
- The integration builds and uses the warning feature model as intended.
- Any required adjustments for downstream consumption are identified and tracked.
- `reference_integration` serves as a validation reference for follow-up adopters.

### How

- Add compiler warning feature integration to `reference_integration`.
- Update the integration to consume the new warning policy from `score_cpp_policies`.
- Verify that the integration behaves as intended with the migrated feature model.
- Use the integration outcome to identify adoption gaps before broader rollout.