docs(pm): say what the widened record read costs, and what stayed C6's

The header's budget and doc-shape paragraphs, `verdictThreadRows`'s declared
limit and the exit table now describe the reads a `--pair` run actually makes,
and the success line no longer prescribes a citation to a pair that owes no
clear.

Claude-Session: https://claude.ai/code/session_01HZfg2AwVX191qCizp88gQr
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

scripts/pm/check-clause2-carriers.mjs

@@ -4048,8 +4048,8 @@ function renderPair(pair, repo, pairs = null) {
               'both carriers agree'
             : 'readable in the fixed spelling and both carriers agree') +
         (record
-          ? ', and a review of record names this head (the note above says which comment to cite; ' +
-            'existence, not the verdict)'
+          ? ', and a review of record names this head (the note above says which comment it is, and ' +
+            'whether this pair owes anything about it; existence, not the verdict)'
           : '') +
         (widening.state === 'clean'
           ? ', and its diff carries no widening tell. ⚠️ A tell is not a proof and its absence is not one either.'