feat: add event-driven cloud processing architecture

[cr-shah]

Summary

• add S3/local raw-event storage, Lambda ingestion, versioned SQS messages, retry and dead-letter handling
• add an idempotent container worker that reuses existing validation, feature, scoring, and expected-loss logic
• separate PostgreSQL operational state from Snowflake analytical history with incremental MERGE loading
• add Prefect batch flows, Terraform infrastructure, secure configuration, structured logging, and extensive deployment documentation

Reliability and security

• PostgreSQL event and transaction uniqueness prevents duplicate financial and analyst-review records
• Snowflake MERGE makes analytical retries idempotent
• failed SQS messages remain available for retry and DLQ routing
• S3 versioning, encryption, public-access blocking, least-privilege IAM, ignored state/secrets, and Docker context exclusions are included

Verification

• 73 tests passed with 66% aggregate coverage
• Ruff lint and formatting passed
• GitHub Actions CI passed
• dependency lock and installed-package checks passed
• Lambda deployment package built successfully
• Terraform HCL and Docker Compose YAML parsed successfully
• staged secret scan found no credentials
• fresh 12,000-row demo generation matched checked-in artifacts byte for byte