Add unreachable status handling to ServerCard

- Gray out unreachable servers with 50% opacity
- Disable click interaction for unreachable servers
- Show "Nicht erreichbar" badge

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

gsm-frontend/src/components/ServerCard.jsx

@@ -107,17 +107,20 @@ export default function ServerCard({ server, onClick, isAuthenticated, displaySe
         return { class: 'badge badge-warning', text: 'Starting...' }
       case 'stopping':
         return { class: 'badge badge-warning', text: 'Stopping...' }
+      case 'unreachable':
+        return { class: 'badge bg-neutral-600 text-neutral-400', text: 'Nicht erreichbar' }
       default:
         return { class: 'badge badge-destructive', text: 'Offline' }
     }
   }
 
   const statusBadge = getStatusBadge()
+  const isUnreachable = server.status === 'unreachable'
 
   return (
     <div
-      className="card card-clickable p-5"
-      onClick={onClick}
+      className={isUnreachable ? "card p-5 opacity-50 cursor-not-allowed" : "card card-clickable p-5"}
+      onClick={isUnreachable ? undefined : onClick}
     >
       {/* Header */}
       <div className="flex items-center justify-between mb-2">