Claim 5: implement + time real EBM<->ARM conversions (O(V^T) vs O(VT), measured)

Verify all 5 claims by exact ARM-EBM enumeration: Prop3.2 bijection (8.9e-16), soft-Bellman, Prop4.1 NLL equiv, Prop48 KL bound, conversion asymmetry

Update logbook: Repro - Autoregressive Language Models are Secretly Energy-Based Models

Update logbook: Repro - Autoregressive Language Models are Secretly Energy-Based Models

Update logbook: Repro - Autoregressive Language Models are Secretly Energy-Based Models