feat: add filtered traffic page to admin dashboard

Add admin page at /admin/filtered-traffic showing domains blocked by the
referrer spam filter with reason badges and date range selector. Helps
operators monitor spam filtering and catch false positives.

app/admin/page.tsx

@@ -15,6 +15,16 @@ export default function AdminDashboard() {
           View all organizations, check billing status, and manually grant plans.
         </p>
       </Link>
+      <Link
+        href="/admin/filtered-traffic"
+        className="block transition-transform hover:scale-[1.02] rounded-2xl border border-neutral-200 dark:border-neutral-800 bg-white dark:bg-neutral-900 p-6 shadow-sm"
+      >
+        <h3 className="text-lg font-semibold text-neutral-900 dark:text-white">Filtered Traffic</h3>
+        <p className="text-sm text-neutral-500 dark:text-neutral-400 mt-1">Monitor blocked referrer spam</p>
+        <p className="text-sm text-neutral-500 dark:text-neutral-400 mt-4">
+          View domains blocked by the spam filter and check for false positives.
+        </p>
+      </Link>
     </div>
   )
 }