SAFETY-39: correct the gain figures, which were not the measured ones

Review found validate.py:288-289 carrying numbers that appear nowhere
else in the PR's evidence and could not be reproduced: over-absorption
"1233 W at slew 1000 and 1344 W at slew 250 ... 1495 W at 0.6, 961 W at
0.3, ~0 W at 0.2". A grep for 1233/1344/1495 found them ONLY in that
comment - the DECISIONS record, the PR body, test_control.py's audit
table and slew_sim's own output all carried the correct ones.

The measured values, from re-running tools/slew_sim.py on the real plant
model at the stated conditions (max_w 5000, 2 s tick, 51 export steps
1.0-4.2 kW): slew column 958 (slew 1000) and 1081 (slew 250); gain column
987 (0.6), 876 (0.3), 435 (0.2).

⚠️ "~0 W at 0.2" WAS WRONG IN THE UNSAFE DIRECTION. It invited a future
reader to conclude that dropping gain to 0.2 removes over-absorption. It
does not: 435 W remains, which is 44 % of the figure at 0.6, not zero.
The corrected text says so at the line rather than leaving a round number
to be trusted.

The conclusion the paragraph draws is unchanged and still holds on the
measured figures: over-absorption is flat in slew_w and falls in gain, so
`gain` is the constant that would have to move, and SAFETY-39
deliberately does not move it.

No behaviour change; comment only. Full suite: 21 passed, 0 failed.

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

goodwe_controller/app/validate.py

@@ -285,8 +285,9 @@ WHAT IS DELIBERATELY *NOT* REFUSED, because it is untidy rather than unsafe:
     than the rule would have been. On admin/goodwe's rig, over a family of 51
     export steps from 1.0 to 4.2 kW at `max_w: 5000` and a 2 s tick, the
     over-absorption - peak battery power beyond what the site actually needed -
-    is FLAT in `slew_w`: 1233 W at slew 1000 and 1344 W at slew 250. It falls
-    monotonically in `gain`: 1495 W at 0.6, 961 W at 0.3, ~0 W at 0.2. The
+    is FLAT in `slew_w`: 958 W at slew 1000 and 1081 W at slew 250. It falls
+    in `gain`: 987 W at 0.6, 876 W at 0.3, 435 W at 0.2 - a real reduction, but
+    NOT to zero, and the 0.2 figure is the one worth not rounding away. The
     reason is structural and is visible in control.py: `slew_w` bounds the
     OUTPUT, while the integrator accumulates `gain * error` per cycle and is
     bounded only by `integrator_max_w`. At gain 0.6 into a 3.4 kW error the