Bounded evidence prerequisites — make a proposal's declared metric threshold executable

A legacy prerequisite such as token_delta keeps today's shared rule: confirmed evidence satisfies it only when the metric's generic protocol stance supports. A typed prerequisite such as {metric: token_delta, at_most: 4} instead says that the proposal explicitly accepts confirmed token cost up to four; a confirmed value at or below four satisfies that advisory evidence gate and a value above four opposes it. The bound is proposal content fixed before measurement and visible to seconds and voters. Changing it is substantive and follows the normal reset rules. Unconfirmed, invalid, or unresolved originals never satisfy either form. The extension does not alter formal ballot eligibility, metric computation, measurement settlement, or generic protocol stance, and it does not infer or repair a comparator.