feat: Add cluster page navigation

- Add EPYC Cluster card to landing page (first position, purple/pink gradient)
- Add back button to cluster page (animated left arrow, links to dashboard)
- Update landing page grid layout (lg:grid-cols-3 xl:grid-cols-4 for 7 cards)
- Complete bidirectional navigation: dashboard ↔ cluster monitoring

Navigation features:
- Cluster card: 🖥️ icon, "Monitor distributed parameter exploration" description
- Back button: Animated hover effect (arrow slides left, color transitions)
- Responsive grid: 2 cols (mobile), 3 cols (tablet), 4 cols (desktop)
- Consistent styling with existing navigation cards

app/cluster/page.tsx

@@ -113,6 +113,17 @@ export default function ClusterPage() {
   return (
     <div className="min-h-screen bg-gray-900 text-white p-8">
       <div className="max-w-7xl mx-auto">
+        {/* Back Button */}
+        <a
+          href="/"
+          className="inline-flex items-center text-blue-400 hover:text-blue-300 mb-6 transition-colors group"
+        >
+          <svg className="w-5 h-5 mr-2 group-hover:-translate-x-1 transition-transform" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+            <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M15 19l-7-7 7-7" />
+          </svg>
+          <span className="font-medium">Back to Dashboard</span>
+        </a>
+
         <div className="flex justify-between items-center mb-8">
           <h1 className="text-3xl font-bold">🖥️ EPYC Cluster Status</h1>
           <button