SAFETY-31: the grid is 42, not 90, and the wrong number was in the failure text

Review reproduced every figure in both PRs except one, and rejected on it.

⚠️ "0 of 90 GAINS x SPLITS combinations produce opposing shares" - the SUBSTANCE
is right and review re-measured it, but the DENOMINATOR is invented. sitesim.py
declares GAINS with 7 entries and SPLITS with 6: the grid is 42. 90 is not even
divisible by 7, so no reading of "GAINS x SPLITS" reaches it. It is almost
certainly TEST-20`s RUN count (84 + 6), which is a different quantity that
happened to be nearby.

⚠️ AND THE WORST COPY OF IT WAS INSIDE THE `PRECONDITION FAILED` TEXT, so the
next engineer to see this scenario go red would have been handed an
unreproducible measurement as their diagnosis - the exact defect class this
campaign exists to correct, in the failure path where it does the most harm.

Corrected in all seven places. At the failure-text site the denominator is now
`len(GAINS) * len(SPLITS)`, computed rather than typed, so it cannot drift from
the grid again - the same fix test_translations.py already took.

Also N3: a missing blank line was going to render the S3 and M19 paragraphs as
one in DECISIONS.

Re-run after the change: `inject.py two_master_circulation` PASS in 35 s, norig,
no rig lock taken. Add-on suite 26 files, all pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BwRLw7eKYj2byVdwB6kbjU

goodwe_controller/DECISIONS/SAFETY-31-circulating-power.md

@@ -381,6 +381,7 @@ a *larger* worst peak (2250 W) than the modelled plant does (1048 W). The claim
 in the check's own text was wrong. It was corrected against the measurement, the
 plant was pinned as an explicit term, and S3 is red now for a stated reason
 rather than by accident. §3's spread table is that measurement.
+
 **M19 is recorded as a survivor because it was one.** The first battery found no
 check grading what `publish()` does when a per-unit reading is missing, so
 turning *"I do not know"* into *"0 W"* on the one surface an operator actually