feat: add web frontend rules and design quality hook

rules/web/testing.md

@@ -0,0 +1,55 @@
+> This file extends [common/testing.md](../common/testing.md) with web-specific testing content.
+
+# Web Testing Rules
+
+## Priority Order
+
+### 1. Visual Regression
+
+- Screenshot key breakpoints: 320, 768, 1024, 1440
+- Test hero sections, scrollytelling sections, and meaningful states
+- Use Playwright screenshots for visual-heavy work
+- If both themes exist, test both
+
+### 2. Accessibility
+
+- Run automated accessibility checks
+- Test keyboard navigation
+- Verify reduced-motion behavior
+- Verify color contrast
+
+### 3. Performance
+
+- Run Lighthouse or equivalent against meaningful pages
+- Keep CWV targets from [performance.md](performance.md)
+
+### 4. Cross-Browser
+
+- Minimum: Chrome, Firefox, Safari
+- Test scrolling, motion, and fallback behavior
+
+### 5. Responsive
+
+- Test 320, 375, 768, 1024, 1440, 1920
+- Verify no overflow
+- Verify touch interactions
+
+## E2E Shape
+
+```ts
+import { test, expect } from '@playwright/test';
+
+test('landing hero loads', async ({ page }) => {
+  await page.goto('/');
+  await expect(page.locator('h1')).toBeVisible();
+});
+```
+
+- Avoid flaky timeout-based assertions
+- Prefer deterministic waits
+
+## Unit Tests
+
+- Test utilities, data transforms, and custom hooks
+- For highly visual components, visual regression often carries more signal than brittle markup assertions
+- Visual regression supplements coverage targets; it does not replace them