Give the shell one header, a skip link, and a cookie-aware first paint.

Breakpoint clones were still in the tab order, marketing always painted Log in, and at 430px the logo overlay covered Use cases and Learn.

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

tests/components/SkipToContent.test.tsx

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+import "@testing-library/jest-dom/vitest";
+import { describe, expect, it } from "vitest";
+import SkipToContent from "../../app/components/navigation/SkipToContent";
+import { MAIN_CONTENT_ID } from "../../lib/mainContent";
+import { renderWithProviders as render, screen } from "../utils/test-utils";
+
+describe("SkipToContent", () => {
+  it("targets the main landmark", () => {
+    render(<SkipToContent />);
+    const link = screen.getByRole("link", { name: "Skip to content" });
+    expect(link).toHaveAttribute("href", `#${MAIN_CONTENT_ID}`);
+    expect(link).toHaveClass("skip-to-content");
+  });
+});