fix(frontend): encode handle in URL to avoid Next.js routing issues with @ chars

thoughts-frontend/components/remote-user-card.tsx

@@ -38,7 +38,7 @@ export function RemoteUserCard({ actor }: RemoteUserCardProps) {
   return (
     <div className="flex items-center justify-between p-4 border rounded-lg">
       <Link
-        href={`/users/@${actor.handle}`}
+        href={`/users/${encodeURIComponent("@" + actor.handle)}`}
         className="flex items-center gap-3 hover:opacity-80"
       >
         <UserAvatar src={actor.avatarUrl} alt={actor.displayName ?? actor.handle} />