Add basic async worker and Kafka producer (HIGH) - add Kafka producer on order create and simple Kafka consumer worker

[raggopaluni]

Goal:

• Publish an order-created event to Kafka and set up a local worker that consumes this event and simulates a workflow.

Tasks:

• Add requirements: kafka-python or confluent-kafka.
• In POST /orders: after persisting, produce a Kafka message to topic orders.
• Add worker/consumer.py that consumes topic orders and logs event.
• In docker-compose: add a single-node Kafka (use wurstmeister or bitnami images) or use local lightweight substitute if needed.
• Worker must update Postgres order status to "processing" -> "completed" after simulated delays.

Acceptance criteria:

• Creating an order emits a Kafka message.
• Worker consumes message and updates order status in Postgres.