Add AWS Comprehend prompt redaction utility

[josemariano-hub]

Summary\n- add AwsComprehendRedactor for AWS Comprehend DetectPiiEntities without adding AWS SDK dependencies\n- expose helpers to redact raw prompts and chat options before chaining into existing AI endpoint calls\n- add unit coverage with mocked Comprehend responses\n- add a Jsonnet-based example showing PII redaction before an OpenAI call\n\n/claim #290\n\nCloses #290\n\n## Demo\n- https://raw.githubusercontent.com/josemariano-hub/edgechains-demo-assets/main/edgechains-aws-comprehend-demo.mp4\n\n## Verification\n- npx vitest run awsComprehendRedactor.test.ts\n- npm run build

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Include session token in SigV4 signed headers

When temporary AWS credentials are used (AWS_SESSION_TOKEN/sessionToken), this signer adds X-Amz-Security-Token to the outbound headers later but does not include it in canonicalHeaders/signedHeaders, so the computed signature no longer matches the actual request headers. In IAM role-based environments (Lambda/ECS/EKS/SSO), Comprehend calls can fail with signature/auth errors, which breaks redaction entirely for those deployments.

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[josemariano77]

I have read the Arakoo CLA Document and I hereby sign the CLA

[josemariano-hub]

recheck

[josemariano-hub]

Updated the PR to include AWS session tokens in the SigV4 canonical/signed headers when temporary credentials are used.\n\nVerification after the update:\n- npx vitest run awsComprehendRedactor.test.ts\n- npm run build\n- GitHub checks: CLAAssistant, changes, and js passing

[josemariano-hub]

Added the requested short demo video for the AWS Comprehend redaction flow:\n\nhttps://raw.githubusercontent.com/josemariano-hub/edgechains-demo-assets/main/edgechains-aws-comprehend-demo.mp4\n\nIt shows:\n- AwsComprehendRedactor redacting PII from prompts/messages\n- mocked Vitest coverage passing\n- the runnable Jsonnet example under examples/aws-comprehend-redaction\n- build/test verification\n\nVerification:\n- npx vitest run awsComprehendRedactor.test.ts\n- npm run build