### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate. Related but NOT the same: #29189 (surfaces AWS's `x-amzn-RequestId` *response* header into LiteLLM's own logs/OTEL — doesn't touch the outbound request) and #31985/merged (adds `trace`/`guardrailConfig` support for Bedrock used *as the inference provider* via the InvokeModel route, `llms/bedrock/chat/invoke_transformations/`). Neither touches the standalone Bedrock Guardrails integration (`proxy/guardrails/guardrail_hooks/bedrock_guardrails.py`), which is the subject of this issue.

### What happened?

The standalone AWS Bedrock Guardrails proxy integration (configured via `guardrailIdentifier` + `guardrailVersion` in `litellm_params`, usable against any inference provider/model — not just Bedrock-hosted models) never sends AWS's `trace` parameter on its `ApplyGuardrail` API call. As a result, guardrail evaluations routed through LiteLLM produce no trace/assessment detail on the AWS side (CloudWatch / AWS console guardrail logs…