document the single UI stack and strengthen resize focus coverage

tests/review-ui-foundation.e2e.test.mjs

@@ -133,6 +133,16 @@ test(
         await page.getByRole("dialog", { name: "主导航", exact: true }).count(),
         0,
       );
+      const link = navigation(page).getByRole("link", {
+        name: "SSH 密钥",
+        exact: true,
+      });
+      await link.focus();
+      assert.equal(
+        await link.evaluate((element) => element === document.activeElement),
+        true,
+        "Desktop navigation is focusable after the overlay closes",
+      );
       return {
         desktopAt1025: true,
         overlayAt1024: true,