feat(landing): redesign hero + editorial layout with Atkinson Hyperlegible

Recover and commit the landing-page redesign that had been sitting
uncommitted in the working tree: refreshed dark palette (adjusted
--lp-bg-alt, electric-blue accent), Atkinson Hyperlegible Next display
+ body type, and editorial hero/section layout in LandingPage.tsx, with
the matching font preload in index.html.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/index.html

@@ -10,7 +10,7 @@
     <!-- Google Fonts -->
     <link rel="preconnect" href="https://fonts.googleapis.com">
     <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
-    <link href="https://fonts.googleapis.com/css2?family=Bricolage+Grotesque:wght@400;600;700;800&family=IBM+Plex+Sans:wght@400;500;600&family=JetBrains+Mono:wght@400;500&display=swap" rel="stylesheet">
+    <link href="https://fonts.googleapis.com/css2?family=Atkinson+Hyperlegible+Next:ital,wght@0,400;0,500;0,600;0,700;0,800;1,400;1,700&family=Atkinson+Hyperlegible+Mono:wght@400;500&family=Bricolage+Grotesque:wght@400;600;700;800&family=IBM+Plex+Sans:wght@400;500;600&family=JetBrains+Mono:wght@400;500&display=swap" rel="stylesheet">
 
     <!-- PWA Icons -->
     <link rel="apple-touch-icon" href="/icons/app-icon-gradient.svg" />