Add ember-best-practices skill

.agents/skills/ember-best-practices/rules/a11y-automated-testing.md

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+---
+title: Use ember-a11y-testing for Automated Checks
+impact: HIGH
+impactDescription: Catch 30-50% of a11y issues automatically
+tags: accessibility, a11y, testing, ember-a11y-testing
+---
+
+## Use ember-a11y-testing for Automated Checks
+
+Integrate ember-a11y-testing into your test suite to automatically catch common accessibility violations during development. This addon uses axe-core to identify issues before they reach production.
+
+**Incorrect (no accessibility testing):**
+
+```glimmer-js
+// tests/integration/components/user-form-test.js
+import { module, test } from 'qunit';
+import { setupRenderingTest } from 'ember-qunit';
+import { render, fillIn, click } from '@ember/test-helpers';
+import UserForm from 'my-app/components/user-form';
+
+module('Integration | Component | user-form', function (hooks) {
+  setupRenderingTest(hooks);
+
+  test('it submits the form', async function (assert) {
+    await render(<template><UserForm /></template>);
+    await fillIn('input', 'John');
+    await click('button');
+    assert.ok(true);
+  });
+});
+```
+
+**Correct (with a11y testing):**
+
+```glimmer-js
+// tests/integration/components/user-form-test.js
+import { module, test } from 'qunit';
+import { setupRenderingTest } from 'ember-qunit';
+import { render, fillIn, click } from '@ember/test-helpers';
+import a11yAudit from 'ember-a11y-testing/test-support/audit';
+import UserForm from 'my-app/components/user-form';
+
+module('Integration | Component | user-form', function (hooks) {
+  setupRenderingTest(hooks);
+
+  test('it submits the form', async function (assert) {
+    await render(<template><UserForm /></template>);
+
+    // Automatically checks for a11y violations
+    await a11yAudit();
+
+    await fillIn('input', 'John');
+    await click('button');
+    assert.ok(true);
+  });
+});
+```
+
+**Setup (install and configure):**
+
+```bash
+ember install ember-a11y-testing
+```
+
+```javascript
+// tests/test-helper.js
+import { setupGlobalA11yHooks } from 'ember-a11y-testing/test-support';
+
+setupGlobalA11yHooks(); // Runs on every test automatically
+```
+
+ember-a11y-testing catches issues like missing labels, insufficient color contrast, invalid ARIA, and keyboard navigation problems automatically.
+
+Reference: [ember-a11y-testing](https://github.com/ember-a11y/ember-a11y-testing)