Fix datetime.UTC to timezone.utc across agent-coordinator codebase

- Changed datetime.UTC to timezone.utc in advanced_ai.py
- Changed datetime.UTC to timezone.utc in realtime_learning.py
- Changed datetime.UTC to timezone.utc in jwt_handler.py
- Changed datetime.UTC to timezone.utc in distributed_consensus.py
- Changed datetime.UTC to timezone.utc in exceptions.py
- Changed datetime.UTC to timezone.utc in alerting.py
- Changed datetime.UTC to timezone.utc in communication.py
- Changed datetime.UTC to timezone.utc in message_types.py
- Updated imports from `datetime import

docs/apps/marketplace-service/README.md

@@ -0,0 +1,18 @@
+# Marketplace Service
+
+**Marketplace Service Documentation**
+
+This service provides the GPU marketplace for compute resource trading.
+
+## Features
+- Resource listing and discovery
+- Bidding and offer management
+- Transaction processing
+
+## Related Documentation
+- [GPU Service](../gpu-service/README.md)
+- [Marketplace Bidding Scenario](../../scenarios/08_marketplace_bidding.md)
+
+---
+
+*Last Updated: 2026-05-02*