feat(ai): integrate AWS Comprehend PII redaction and observable chaining (#290)

[tivince82]

/claim #290

Summary of Changes

This PR integrates Amazon Comprehend into the EdgeChains JavaScript/TypeScript SDK (@arakoodev/edgechains.js) as a chainable redaction utility to detect and sanitize PII before prompts reach LLM endpoints.

1. AwsComprehendRedactor:

   • Wraps AWS SDK v3 @aws-sdk/client-comprehend (DetectPiiEntitiesCommand).
   • Supports dependency injection of the client for offline testing in CI/CD without AWS credentials.
   • Deterministic descending offset replacement to avoid index corruption.
   • Configurable masking modes (ENTITY_TYPE, REDACTED_LABEL, ASTERISK, CUSTOM).
   • Confidence thresholding (minScore) and entity allowlist/blocklists.
   • Fail-closed security mode by default to prevent leaking raw prompts if detection fails.
   • Fallback regex guards for critical identifiers (SSN, Email, Phone, Credit Cards).

2. AwsComprehendRedactionChain & Reactive Observables:

   • Cold RxJS Observables (.redact, .redactPrompt, .chat).
   • Custom RxJS operators (redactPiiOperator(), redactChatOptionsOperator()).
   • Direct chaining with OpenAI, GeminiAI, and LlamaAI endpoints.

3. Unit Tests:

   • Added 14 comprehensive unit tests in Vitest covering entity detection, masking formats, score filtering, Unicode handling, fail-closed behavior, and RxJS observable chaining.

4. Example Demo:

   • Added JS/edgechains/examples/comprehend-redaction/ showcasing standalone redaction, observable streams, and endpoint chaining.

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Demo Walkthrough

• Video Walkthrough (MP4): Download demo.mp4

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Verification

# 1. SDK Unit tests (14/14 passing):
cd JS/edgechains/arakoodev && npx vitest run src/ai/src/tests/awsComprehendRedaction.test.ts

# 2. Runnable example demo:
cd ../examples/comprehend-redaction && npm start

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[tivince82]

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[tivince82]

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