v10.16.0 — small-N pole certificates (P1i)

Direct per-case certificates for 52 reduced a/N with 3<=N<=16 (excluding N=4, covered elsewhere, and N=6, structurally open). Adds one new U/V pole point outside the previously-stated arc: a/N=2/13. The N=6 case is diagnosed as structurally unclosable by this method (tie height T<0 against a head term of rate 0), not merely unproved. Reviewed by Reviewer AE (CORRECT, one wording fix).