Fixes #290

Summary

• add an AwsComprehendRedactor AI utility backed by @aws-sdk/client-comprehend
• support prompt redaction with typed placeholders, masking mode, confidence/type filters, and RxJS observable chaining
• export the redactor from the JS AI package
• add focused tests with a mocked Comprehend client
• add a jsonnet-driven example under examples/aws-comprehend-redaction

Verification

• bun test src/ai/src/tests/aws-comprehend/awsComprehendRedactor.test.ts
• bun run build

/claim #290