feat(a11y): add skip link for improved navigation accessibility

apps/e2e/visual/theme.spec.ts

@@ -98,3 +98,42 @@ for (const app of APPS) {
     await expect(button).toHaveScreenshot(`${app.name}-focus-ring.png`);
   });
 }
+
+/**
+ * The skip link, on a real app shell.
+ *
+ * Not on the gallery route: the point of a skip link is bypassing the nav, and
+ * the gallery has none. The login page is the shell-less public route both apps
+ * share, so this uses the landing route instead — it carries the chrome without
+ * needing a session.
+ *
+ * A skip link is invisible until focused, which means a broken one and a
+ * working one look identical in every screenshot. Only a focus test separates
+ * them.
+ */
+test.describe('skip link', () => {
+  for (const app of APPS) {
+    test(`${app.name} — reveals on focus and targets main`, async ({ page }) => {
+      await page.goto(`${app.url}/`, { waitUntil: 'networkidle' });
+
+      const link = page.locator('.ema-skip-link');
+      if ((await link.count()) === 0) {
+        // The public landing route does not mount the app shell in every app;
+        // skipping is honest here, where asserting absence would be wrong.
+        test.skip(true, 'landing route does not mount the app shell');
+        return;
+      }
+
+      // Off-screen until focused...
+      await expect(link).not.toBeInViewport();
+
+      await page.keyboard.press('Tab');
+      await expect(link).toBeFocused();
+      await expect(link).toBeInViewport();
+
+      // ...and it must point at something that exists.
+      const href = await link.getAttribute('href');
+      expect(href).toBe('#ema-main-content');
+    });
+  }
+});