fix: SSR crash — QueryClient in useState, mounted guard for auth hydration

app/(app)/layout.tsx

@@ -1,6 +1,6 @@
 'use client';
 
-import { useEffect } from 'react';
+import { useEffect, useState } from 'react';
 import { useRouter } from 'next/navigation';
 import { useAuthStore } from '@/lib/auth-store';
 import Sidebar from '@/components/layout/sidebar';
@@ -9,16 +9,22 @@ import Topbar from '@/components/layout/topbar';
 export default function AppLayout({ children }: { children: React.ReactNode }) {
   const router = useRouter();
   const accessToken = useAuthStore((s) => s.accessToken);
+  // Wait for zustand to hydrate from localStorage before checking auth
+  const [mounted, setMounted] = useState(false);
 
   useEffect(() => {
-    if (!accessToken) {
+    setMounted(true);
+  }, []);
+
+  useEffect(() => {
+    if (mounted && !accessToken) {
       router.replace('/login');
     }
-  }, [accessToken, router]);
+  }, [mounted, accessToken, router]);
 
-  if (!accessToken) {
-    return null;
-  }
+  // Show nothing until hydrated (prevents flash redirect)
+  if (!mounted) return null;
+  if (!accessToken) return null;
 
   return (
     <div className="flex min-h-screen" style={{ backgroundColor: '#F8FAFC' }}>