feat(ai): add AWS Comprehend prompt redaction

[genaaredes-ui]

Resolves #290

Summary

• Add ComprehendRedactor for AWS Comprehend DetectPiiEntities with SigV4 signing.
• Redact PII before passing prompts to any downstream endpoint via protect.
• Add mocked tests and a credential-free example.

Validation

• TypeScript strict compile for the new utility passed.
• Mocked Node integration passed: email [REDACTED].
• No AWS credentials are included.

Note

The issue requests a Loom demonstration. This PR includes the runnable example and does not include a Loom URL yet.

[github-actions]

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