Wait for the application, not the clock, in the strict QA set

The probe exposes settled() and the first-frame outcome; scripts/qa/ready.mjs
waits for drawn frames with the camera at rest and for a pick at the click
position, with a deadline and its reason in the error. The strict scenarios
use these instead of fixed pauses and loading-screen polling, and the
hidden-switch scenario checks how the loading screen was lifted instead of
how long it took.

Each switch scenario now records a draw ledger per engine and runs a
contract monitor; both write to the scenario's evidence file only, with an
empty allowlist until browser runs show what differs on purpose.

scripts/qa-wind-engine-switch.mjs

@@ -1,3 +1,4 @@
+import { whenSettled } from './qa/ready.mjs';
 import sharp from 'sharp';
 import assert from 'node:assert/strict';
 import {
@@ -95,7 +96,7 @@ await strict.run({}, async (b) => {
         window.qaWind.getRowControls().summary.reading?.speed === 10,
       { timeout: 90000 },
     );
-    await new Promise((resolve) => setTimeout(resolve, 800));
+    await whenSettled(p);
     const check = await p.evaluate(() => {
       const { dataManager } = window.__godsEyeView;
       const mod = dataManager.layers.get('wind').module;
@@ -161,7 +162,7 @@ await strict.run({}, async (b) => {
   const frozen = await p.evaluate(
     () => window.qaWind.getDiagnostics().gpu.phaseSeconds,
   );
-  await new Promise((resolve) => setTimeout(resolve, 250));
+  await whenSettled(p);
   await strict.check(
     p,
     'wind',