Add full-scale claim evidence and release gate

Reproduce Prop 4.1 on 2D grid: flow mixing recovers linear scalarization exactly (L1=0), distortion constant, linear-specific, graceful non-linear degradation (L1=0.107)

Update logbook: Repro - Routing by Reaching

Composition suite on pre-trained neural GFlowNets: 524 training-free adaptations, exact recovery 4.8e-16

Update logbook: Repro - Routing by Reaching