Complete Unit 15.10 Implement OpenTelemetry exception handling in layer validation

- Added targeted exception handling around validate_layer_imports() to prevent Lambda runtime failure
- Catches StopIteration and ImportError from OpenTelemetry context loading issue on Python 3.12
- Logs detailed warning while skipping validation to preserve webhook processing
- Maintains core multi-agent functionality during production runs
- Provides diagnostic output for future troubleshooting
- Addresses critical 500 Internal Server Error affecting API Gateway responses

Result: Restores production stability while allowing future investigation of OpenTelemetry compatibility with Python 3.12.

Author: robertoallende