Add Amazon Comprehend PII redaction utility

[oomp]

Summary

• Add a PIIRedactor utility backed by Amazon Comprehend DetectPiiEntities.
• Export PIIRedactor from the AI package.
• Add optional PII redaction for OpenAI and Gemini prompts/messages before provider calls.

Test Plan

• npx tsc -p tsconfig.json --noEmit
• npx vitest run src/ai/src/tests/piiRedactor.test.ts --pool=threads --poolOptions.threads.singleThread=true

Closes #290

[github-actions]

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