Remove backend-side Athena integration (architectural violation)

The Athena Decision Service integration was incorrectly placed in the
backend (consumer.py). This violates the separation of concerns:
- Backend handles recommendations (ML predictions, SSE routing)
- Agent handles instructions (user confirmation, microscope control)

Changes:
- Remove athena_api imports from consumer.py
- Remove athena_client initialization and helper functions
- Remove Athena calls from prediction handlers
- Delete WIP documentation file

Bug fixes retained from original PR:
- Fix CurrentQualityPrediction.value assignment (was overwriting object)
- Fix session.add_all() for list of predictions (was using add())

Agent-side Athena integration tracked in issue #198.

Author: vredchenko