Implemented AWS Comprehend integration to allow for PII (Personally Identifiable Information) detection and redaction within the JS SDK.

Changes:

• Added Comprehend class in src/ai/src/lib/aws/comprehend.ts providing detectPiiEntities and redact methods.
• Integrated Comprehend into the main AI module exports.
• Added @aws-sdk/client-comprehend as a dependency.
• Included test scripts to verify the implementation.

Closes #290 /claim #290