Add AWS Comprehend PII redaction support

[alejandrorivas-pixel]

Summary

• add an AWSComprehend utility to @arakoodev/edgechains.js/ai using the official AWS Comprehend client
• support PII detection, score/entity filtering, custom redaction replacements, containsPii(), and redactPrompt()
• add redactPromptOptions() and asPromptMiddleware() so prompt/message options can be redacted before existing endpoint calls
• keep ComprehendPIIRedactor as a compatibility alias
• add Vitest coverage for default redaction, filtered custom replacement behavior, prompt-option redaction, and the alias
• add an aws-comprehend-redaction Jsonnet example with prompt/config outside TypeScript

/claim #290

Closes #290.

Validation

• npx vitest run src/ai/src/tests/comprehendPIIRedactor.test.ts
• npm run build in JS/edgechains/arakoodev
• npm run build in JS/edgechains/examples/aws-comprehend-redaction after building the local package

[github-actions]

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[alejandrorivas-pixel]

/claim #290