feat: add model contract validation workflow

[hyeokjun32]

Summary

• Added a validation package for presets, model contracts, COCO annotation loading, structural checks, and evaluation reports.
• Extended evaluate-detection with yolov8_coco preset, optional model_contract.json, COCO annotations, skipped-accuracy handling, and JSON/Markdown/HTML report outputs.
• Added normal/problem validation demo fixtures and tests for contract, preset, report, and CLI behavior.

Validation

• poetry run python3 -m pytest tests/test_validation_contracts.py tests/test_evaluate_detection.py -q
• poetry run python3 -m pytest -q
• poetry run inferedgelab evaluate-detection --help

Impact

• Moves InferEdge toward the documented contract/preset-based validation workflow.
• Keeps evaluation explicit and local-first without claiming arbitrary automatic model scoring.
• Preserves existing evaluate-detection behavior for YOLO txt label workflows.

Notes

• This is not production SaaS work.
• resnet_imagenet and custom_contract remain future preset expansion work.