refactor(frontend): EmptyState + LoadingSkeleton primitives; unified ThoughtForm replaces PostThoughtForm and ReplyForm

thoughts-frontend/app/users/[username]/page.tsx

@@ -44,6 +44,7 @@ export async function generateMetadata({
     },
   };
 }
+import { EmptyState } from "@/components/empty-state";
 import { UserAvatar } from "@/components/user-avatar";
 import { Calendar, Settings } from "lucide-react";
 import { Card } from "@/components/ui/card";
@@ -278,14 +279,7 @@ export default async function ProfilePage({ params }: ProfilePageProps) {
                 />
               ))}
               {thoughtThreads.length === 0 && (
-                <Card
-                  id="profile-card__no-thoughts"
-                  className="flex items-center justify-center h-48"
-                >
-                  <p className="text-center text-muted-foreground">
-                    This user hasn&apos;t posted any public thoughts yet.
-                  </p>
-                </Card>
+                <EmptyState message="This user hasn't posted any public thoughts yet." />
               )}
             </TabsContent>
             {isOwnProfile && (