test,docs: tighten M21, and record what the bucket summary does not say

M21 accepted `subset diffs [Colour_f; Comm_identity_unresolved]`, so a row
with no colour diff at all could be absorbed under a colour citation. The
unresolved allowance existed only for the 22 February rows the previous
commit reverted; with those gone the predicate tightens to exact equality
on Colour_f, matching C18's shape, and stays green.

Records two things the audit's bucket summary did not carry. The effective
dataset is 329, not 328: base 327 plus three overlay Adds minus one
Suppress, so commemoration-of-st-peter and major-litanies fall outside
both buckets despite being in the stated scope, and a suppressed entry is
counted as verified. And the summary says colour was "independently
checked against RG 124" for every entry where much of it is inferred from
the saint's category rather than read -- the per-entry basis column makes
that distinction and the summary line erases it.

Also records that "zero blast radius" holds only for the observed office:
49766 commemoration-colour changes on 8 slugs are real data changes,
invisible because the CLI omits commemoration colour.

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