Add AWS Comprehend PII redaction

[Luvi-1]

/claim #290

Summary

• add an Amazon Comprehend PII redactor for the JavaScript AI package
• support Unicode-safe direct redaction, immutable prompt/message redaction, and RxJS endpoint chaining
• preserve source ordering and abort in-flight Comprehend requests when subscriptions are cancelled
• add mocked Vitest coverage and a credential-free runnable example with an optional real-AWS mode

Validation

• npx tsc -p tsconfig.json --noEmit --incremental false
• npx vitest run src/ai/src/tests/comprehend/comprehendPiiRedactor.test.ts (4 passed)
• example TypeScript check passed
• offline demo output redacted jane@example.com before the endpoint received the prompt
• repository Prettier settings passed for every touched file

Loom

• AWS Comprehend PII redaction demo

Closes #290

[github-actions]

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[Luvi-1]

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