feat(models): selector dispatch for volumetric vs 2D MRI models

feat(models): add 2D resnet18 4-class Alzheimer's MRI inference module

test(mri/model): drop redundant caplog.at_level (direct handler attach is the actual mechanism)

fix(mri/model): warn when label_names length != model output dim (was silent override)

Add project files

feat(models): train-time confidence stats stashed on _neurobridge_train_stats

feat(models): calibration metadata — precision-at-threshold bins on _neurobridge_calibration

feat(models): SHAP top-k explainer for BBB predictions

feat(models): BBB classifier with predict_with_proba uncertainty