revert peak-decline (v2.1): restore v2.0 harvest-at-16 budgets — exp1 9138/2.33B, exp2 7433/1.89B

budget v2.1: peak-decline stop; exp1 8479/2.19B tok, exp2 6887/1.77B tok

round2 v2: per-problem adaptive harvest-at-16 budgets; exp1 9138/2.33B tok, exp2 7433/1.89B tok, exp3 bucket-pure H+2 (lmax 9)