feat(ui): update explore page

uniconnect-app/app/app/explore/page.tsx

+import { Button } from '@/components/ui/button';
+import {
+  Card,
+  CardContent,
+  CardDescription,
+  CardFooter,
+  CardHeader,
+  CardTitle,
+} from '@/components/ui/card';
+import { Input } from '@/components/ui/input';
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from '@/components/ui/select';
+
 export default function ExplorePage() {
-  return <div>ExplorePage</div>;
+  return (
+    <div className='container mx-auto px-4 py-8'>
+      <h1 className='text-4xl font-bold mb-8'>Explore Listings</h1>
+      <div className='flex flex-col md:flex-row gap-4 mb-8'>
+        <Input className='md:w-1/3' placeholder='Search listings...' />
+        <Select>
+          <SelectTrigger className='md:w-1/4'>
+            <SelectValue placeholder='Category' />
+          </SelectTrigger>
+          <SelectContent>
+            <SelectItem value='textbooks'>Textbooks</SelectItem>
+            <SelectItem value='electronics'>Electronics</SelectItem>
+            <SelectItem value='clothing'>Clothing</SelectItem>
+            <SelectItem value='furniture'>Furniture</SelectItem>
+          </SelectContent>
+        </Select>
+        <Button>Search</Button>
+      </div>
+      <div className='grid gap-6 md:grid-cols-2 lg:grid-cols-3'>
+        {[1, 2, 3, 4, 5, 6].map((item) => (
+          <Card key={item}>
+            <CardHeader>
+              <CardTitle>Item Title {item}</CardTitle>
+              <CardDescription>Category • Posted 2 days ago</CardDescription>
+            </CardHeader>
+            <CardContent>
+              <p>
+                Brief description of the item. This could be a textbook,
+                electronic device, or any other item relevant to university
+                students.
+              </p>
+            </CardContent>
+            <CardFooter>
+              <Button>View Details</Button>
+            </CardFooter>
+          </Card>
+        ))}
+      </div>
+    </div>
+  );
 }