Fix legacy weave type usage in eval models

[hsusul]

Summary

• Fixes weave has no attribuite 'type' #211
• Remove legacy @weave.type() decorators from eval model classes
• Keep existing Model inheritance and @weave.op() tracing
• Instantiate EvaluateQualityModel with an explicit system_message keyword

Validation

• uv run python -c "import weave; print(weave.__version__, hasattr(weave, 'type'), hasattr(weave, 'op'), hasattr(weave, 'Model'))"
• uv run python -m py_compile openui/eval/evaluate.py openui/eval/model.py openui/eval/evaluate_weave.py openui/eval/promptsearch.py
• uv run python -c "from openui.eval.evaluate import EvaluateQualityModel, model; from openui.eval.model import EvaluateQualityModel as LegacyEvaluateQualityModel; print(type(model).__name__)"
• git diff --check