feat(ui): replace sidebar with compact top header navigation

- Rewrite MainLayout from vertical sidebar to horizontal header bar
- Brand left, nav tabs center, status indicator right
- Simplify StatusBar to single inline layout (remove collapsed variant)
- Widen content area from max-w-4xl to max-w-6xl
- Remove sidebar-collapsed localStorage persistence

src/routes/index.tsx

@@ -9,7 +9,7 @@ import { useTranslation } from 'react-i18next';
 
 function HomePage() {
   return (
-    <div className="container mx-auto max-w-4xl p-6">
+    <div className="container mx-auto max-w-6xl p-6">
       <CloudAccountList />
     </div>
   );