feat(a11y): wire flash-clamp into autoScrub; document 3-flash/sec audit

Clamp each per-altitude step to the WCAG 2.3.1 floor (no-op at 1200ms, guards
a future lowering). Audit: #black fade + audio crossfade can't exceed 3/sec, no
clamp needed. boot() now seeds the gate-dismissed flag (returning visitor) so
the run-sim test isn't blocked by the new interstitial.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

simulator/e2e/tests/altitude-lock.spec.ts

@@ -10,7 +10,10 @@ import { test, expect, Page } from "@playwright/test";
 // ("<scale> · <clip>  (i/n)").
 
 async function boot(page: Page) {
-  await page.addInitScript(() => localStorage.setItem("hef.devMode", "1"));
+  await page.addInitScript(() => {
+    localStorage.setItem("hef.devMode", "1");
+    localStorage.setItem("hef.motionWarnDismissed", "1"); // returning visitor: skip the photosensitivity gate
+  });
   await page.goto("/");
   // Wait for the "Loading Universe" preload to finish (splash gets class "done").
   await page.waitForFunction(