feat: Introduce and integrate a mobile back button component across agent and user profile pages.

src/components/layout/MobileBackButton.tsx

@@ -0,0 +1,36 @@
+'use client';
+
+import { useRouter } from 'next/navigation';
+
+interface MobileBackButtonProps {
+  label?: string;
+  fallbackHref?: string;
+}
+
+export function MobileBackButton({ label, fallbackHref }: MobileBackButtonProps) {
+  const router = useRouter();
+
+  const handleBack = () => {
+    if (window.history.length > 1) {
+      router.back();
+    } else if (fallbackHref) {
+      router.push(fallbackHref);
+    } else {
+      router.push('/');
+    }
+  };
+
+  return (
+    <button
+      onClick={handleBack}
+      className="lg:hidden flex items-center gap-2 mb-4 hover:opacity-70 transition-opacity cursor-pointer"
+    >
+      <svg width="20" height="20" viewBox="0 0 24 24" fill="none">
+        <path d="M19 12H5M5 12L12 19M5 12L12 5" stroke="#00293D" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round"/>
+      </svg>
+      {label && (
+        <span className="font-fractul font-medium text-[14px] text-[#00293D]">{label}</span>
+      )}
+    </button>
+  );
+}