011 T2: `nflib/bd.py` seam + fake + tests + local JSONL export chokepoint nf-tvc.2 ← Beads

closed priority 2 task unassigned activesession:011-seam

From 011-task-tracking-on-beads.md's task table (design 011). - Note: prefer after T1; mirrors nflib.gh.Gh