Implement schema validation for YAML configuration files

[moshesham]

Problem

YAML configuration files (config.yml, questions_config.yml) are loaded but not validated against a schema. Invalid configurations cause runtime errors with poor error messages.

Impact

• Invalid config causes runtime errors
• Poor error messages when config is wrong
• Hard to debug configuration issues
• No validation feedback for contributors

Tasks

• Create infra/config/schemas.py with JSON schemas
• Add jsonschema to requirements.txt
• Update DataGenerator.load_yaml_config() to validate
• Update question loading to validate questions_config.yml
• Add unit tests for schema validation
• Add tests for invalid configurations
• Document configuration format in docs/
• Add example configurations with comments

References

• PROJECT_REVIEW.md Issue Implement input validation in DataGenerator #16