Add Playwright e2e suite for the landing page

- playwright.config.ts: desktop (1440) + mobile (Pixel 5) projects, static
  webServer over the exported out/; a PW_CHROME env override for the browser
- tests/e2e: render + all core sections, tracked download hrefs with no R2
  exposure, the live counter (mocked function), theme toggle, image loading,
  zero console errors, and responsive nav (desktop links / mobile menu reveal)
- navbar: hide the closed mobile menu with `invisible` so its links stay out of
  the tab order and the accessibility tree, not merely clipped
- add the test:e2e script and ignore test-results/ + playwright-report/

landing/components/layout/navbar.tsx

@@ -90,7 +90,9 @@ export function Navbar() {
         id="mobile-nav"
         className={[
           "overflow-hidden border-b transition-all duration-300 ease-[cubic-bezier(0.22,1,0.36,1)] md:hidden",
-          mobileOpen ? "max-h-72 border-[var(--border)] bg-[var(--bg)]/95 backdrop-blur-xl" : "max-h-0 border-transparent",
+          mobileOpen
+            ? "visible max-h-72 border-[var(--border)] bg-[var(--bg)]/95 backdrop-blur-xl"
+            : "invisible max-h-0 border-transparent",
         ].join(" ")}
       >
         <Container className="flex flex-col gap-1 pb-4 pt-1">