Model Evaluator Block

Evaluate a selected classifier over a selected labeled dataset via useEvaluateModel, reporting accuracy plus macro precision/recall/F1, run duration, and a color-coded confusion matrix, with completed/total progress and cancel, JSON export, and clear-results. Keeps one justified local file (datasets.ts) holding the labeled evaluation datasets and the radio-card selector, too large to inline without harming readability (design D5). No model bytes download until an explicit in-block action.