tooling(pm): give H22's pinned closed-update divisor the staleness alarm H8 carries (#16406)

H22's page budget converts to a coverage-in-days by dividing by
MEASURED_CLOSED_ISSUE_UPDATES_PER_DAY, a hand measurement carrying its own
date and nothing else. Re-measured on 2026-09-06 the board ran ~312
closed-issue updates/day over 40 pages and ~414 over the leading 12, against
a pin of 188.3 -- a factor of 1.66 to 2.2 accumulated in six days, announced
by no run.

H8 has carried a mechanical alarm for exactly this shape since #13499. Apply
it rather than copy it: the observed-rate reader becomes generic over the
stamp it counts (observedMergeRatePerDay delegates to it, byte-identical),
classifyRatePremise takes a premise descriptor so the band, the horizon and
the three verdicts are shared by construction, and the closed pass reports
the update rate it observed from the pages it already read. The census clause
states the pinned rate, the observed one, the factor and the act, on every
run and in every state.

The pin is CHECKED, never overwritten -- H8's rule. The act it names is a
hand re-measure and re-pin.

Self-test: 2588 -> 2636 cases, exit 0.


Claude-Session: https://claude.ai/code/session_019RfFHiRCSs3JXLK4cwcfox

Co-authored-by: Claude <noreply@anthropic.com>

Author: os-steve