feat(mobile): optimize mobile layout, navigation, and spacing

- Implement MobileBottomNav for native thumb-optimized usage
- Simplify Header overlay on mobile
- Add dynamic max() padding to ReferencesSlider for mobile view
- Condense vertical spacing in Footer for mobile devices
- Update layout.tsx to pad main content for bottom nav

app/[locale]/layout.tsx

@@ -1,5 +1,6 @@
 import { Footer } from '@/components/layout/Footer';
 import { Header } from '@/components/layout/Header';
+import { MobileBottomNav } from '@/components/layout/MobileBottomNav';
 import JsonLd from '@/components/JsonLd';
 import SkipLink from '@/components/SkipLink';
 import AnalyticsShell from '@/components/analytics/AnalyticsShell';
@@ -181,10 +182,11 @@ export default async function Layout(props: {
             <PageTransitionShutter />
             <SkipLink />
             <Header navLinks={navLinks} />
+            <MobileBottomNav navLinks={navLinks} currentLocale={safeLocale} />
             
             <main
               id="main-content"
-              className="flex-grow animate-fade-in overflow-visible"
+              className="flex-grow animate-fade-in overflow-visible pb-[90px] md:pb-0"
               tabIndex={-1}
             >
               {children}