Add structured logging config

core/logging.py is referenced as a stub for structured logging setup (configure_logging()). Flesh out real structured logging (e.g. JSON logs, log levels via settings).

Start by reading core/logging.py to understand the current stub. Examine the project's settings to see how log levels are configured. Research Python's logging module and libraries like python-json-logger for structured JSON output. Implement configure_logging() to integrate these, ensuring logs are properly formatted and levels are controlled via settings. Test by running the service and verifying log output.

Written by the indexing model from the issue text.