feat: add policy pages

app/(app)/u/[handle]/mentions/page.tsx

@@ -0,0 +1,25 @@
+"use client";
+
+/**
+ * /u/[handle]/mentions — posts that tag this user.
+ *
+ * Mirror of /u/me/mentions: the tab is wired into the public profile
+ * shell so visitors see an empty state instead of a 404. Will swap to
+ * a real feed once the Mentions feature ships.
+ */
+
+import { AtSign } from "lucide-react";
+import { usePublicProfile } from "../profile-context";
+
+export default function PublicProfileMentionsPage() {
+  const data = usePublicProfile();
+  return (
+    <div className="flex flex-col items-center text-center gap-3 py-12 text-muted-foreground">
+      <AtSign className="size-8" />
+      <p className="text-sm">
+        Posts that tag <span className="text-foreground">@{data.handle}</span>{" "}
+        will appear here. Coming soon.
+      </p>
+    </div>
+  );
+}