Spec brainstorming validato: SAM21 si inserisce tra YOLO bbox e PCA con fallback automatico al path bbox legacy. Tre componenti nuovi (clients/sam21.py, perception/depth_align.py, helper _points_via_sam21) e due modifiche minori (config.yaml, api/_deps.py). Out-of-scope: scan/ object_points, mask UI, nuwa_to_cv_frame cleanup. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>