Add landing page with shadcn/ui and dark mode

components/domain-search-form.tsx

@@ -0,0 +1,37 @@
+"use client";
+
+import { useState, type FormEvent } from "react";
+import { useRouter } from "next/navigation";
+import { Search } from "lucide-react";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+
+export function DomainSearchForm() {
+  const [domain, setDomain] = useState("");
+  const router = useRouter();
+
+  function handleSubmit(e: FormEvent) {
+    e.preventDefault();
+    const trimmed = domain.trim().toLowerCase();
+    if (!trimmed) return;
+    router.push(`/lookup/${encodeURIComponent(trimmed)}`);
+  }
+
+  return (
+    <form onSubmit={handleSubmit} className="flex w-full max-w-xl gap-2">
+      <div className="relative flex-1">
+        <Search className="absolute left-3 top-1/2 size-4 -translate-y-1/2 text-muted-foreground" />
+        <Input
+          type="text"
+          value={domain}
+          onChange={(e) => setDomain(e.target.value)}
+          placeholder="Enter a domain name (e.g. google.com)"
+          className="pl-9 h-11"
+        />
+      </div>
+      <Button type="submit" size="lg">
+        Lookup
+      </Button>
+    </form>
+  );
+}