feat: HomeLab CSS art hero with Proxmox, Switch, NAS

- Add homelab-device-hero component (Proxmox VE + Router icon, Switch, TrueNAS)
- Dashed lines for network connections between devices
- Custom not-found page (replace Next.js 404)
- Homelab page uses CSS hero instead of feature image

Co-authored-by: Cursor <cursoragent@cursor.com>

app/not-found.tsx

@@ -0,0 +1,25 @@
+import Link from 'next/link';
+
+export default function NotFound() {
+  return (
+    <div className="flex min-h-[60vh] flex-col items-center justify-center px-4">
+      <div className="max-w-md text-center">
+        <h1 className="type-display mb-2 text-6xl font-bold text-slate-300 dark:text-slate-600">
+          404
+        </h1>
+        <h2 className="mb-4 text-xl font-semibold text-slate-800 dark:text-slate-200">
+          找不到頁面
+        </h2>
+        <p className="mb-8 text-slate-600 dark:text-slate-400">
+          您造訪的連結可能已失效或不存在。
+        </p>
+        <Link
+          href="/"
+          className="inline-flex items-center rounded-lg bg-slate-800 px-6 py-3 text-sm font-medium text-white transition-colors hover:bg-slate-700 focus:outline-none focus:ring-2 focus:ring-slate-500 focus:ring-offset-2 dark:bg-slate-200 dark:text-slate-900 dark:hover:bg-slate-300"
+        >
+          返回首頁
+        </Link>
+      </div>
+    </div>
+  );
+}