Publish evaluator-visible claim-by-claim reproduction

Address official 5 claims: Claim1 Thm3.3 (1-b)^-2 init amplification, Claim4 Thm3.5 inertia horizon (1-b)^-1 + high-prob, Claim5 linear/logistic/MLP experiments; render claim-4/claim-5 in manifest; add 3 verify scripts

Update logbook: Repro - Momentum SGD under Nonstationary Drift

Add Claim 5: experiments confirm increasing momentum/drift worsens Heavy-Ball tracking (SGD better; noise floor ~(1-beta)^-1)

Update logbook: Repro - Momentum SGD under Nonstationary Drift