feat: add structured JSON logging using structlog (closes #19)

[Anamandla]

Summary

Replaces ad-hoc print() statements with structured JSON logging using structlog, making SentinelPay logs parseable by tools like Grafana Loki and AWS CloudWatch.

Changes

Assignment 12/api/logging_config.py (new file)

• Configures structlog with ISO timestamps, log levels, exception formatting, and JSON rendering to stdout
• Exposes a get_logger() helper for use across the codebase

Assignment 12/handlers/routes/transactions.py

• Added logger.info("transaction_submitted", ...) on every successful transaction submission, including transaction_id, amount, and currency
• Added logger.info("fraud_decision_applied", ...) on every fraud decision, including transaction_id and fraud_score
• Added logger.error("unhandled_error", ...) with traceback for all unhandled 500 errors

requirements.txt

• Added structlog dependency

Sample Log Output

{"timestamp": "2026-06-08T10:00:00Z", "level": "info", "event": "transaction_submitted", "transaction_id": "txn-abc-123", "amount": 500.0, "currency": "ZAR"}
{"timestamp": "2026-06-08T10:00:01Z", "level": "info", "event": "fraud_decision_applied", "transaction_id": "txn-abc-123", "fraud_score": 0.87}

Acceptance Criteria Met

• Every transaction submission produces a JSON log line
• Every fraud decision produces a JSON log line
• Every unhandled error produces an ERROR log with traceback
• Logs written to stdout (Docker-friendly)

Testing

Ran PYTHONPATH=".:../Assignment 10:../Assignment 11" pytest tests/ -v — all 116 tests pass.

Closes #19

[222618698]

sthe

[Teboho66]

All looks good