Improve configuration validation system

[secwexen]

Description

Improve configuration validation across AAPP-MART components.

Current Situation

Configuration files are loaded from:

• configs/default.yaml
• configs/agents.yaml
• configs/predictors.yaml

Invalid configurations may result in runtime errors.

Proposed Improvements

• Add schema-based validation
• Improve validation error messages
• Add missing field detection
• Add configuration validation tests

Related Areas

• src/aapp_mart/
• configs/
• tests/