Add two-stage pipeline: 3D nodule-centre detector (HeatmapUNet3D, CPM 0.629) alongside the existing 2.5D concept-bottleneck characteriser (Student2p5D) with end-to-end inference wrapper.

Add Pulmo: 2.5D concept-bottleneck student model distilled from 3D teacher for lung nodule detection, malignancy classification, and segmentation on LUNA16/LIDC-IDRI

initial commit