feat: Stage 2E physics p95, runtime videos, domain audit, device-test QR

Measure Rapier world.step p95 (~0.2 ms) on GTX 1080, record real route WebMs,
expand runtime/headless hash parity, and document permanent-domain/phone blockers.

Co-authored-by: Cursor <cursoragent@cursor.com>

e2e/helpers.ts

@@ -51,5 +51,5 @@ export async function openPausedCase(page: Page, caseIndex: number, speed: '0.5'
   await page.getByTestId(`demo-case-${caseIndex}`).click();
   await dismissFinished(page);
   await ensurePaused(page);
-  await expect(page.getByTestId('demo-case-label')).toHaveText(`${caseIndex + 1}/11`);
+  await expect(page.getByTestId('demo-case-label')).toHaveText(`${caseIndex + 1}/12`);
 }