fix: Improve admin authentication flow and fix MUI Grid warnings

Authentication fixes:
- Add isAuthenticated() method to ApiClient to check token presence
- Add useEffect in AdminLayout to redirect to login if no token found
- Fix logout to not fail when token is expired/invalid (401)
- Properly handle logout errors by clearing tokens locally
- Clear tokens and redirect to /login on 401 refresh token failure

UI/UX fixes:
- Replace all deprecated MUI Grid v1 with CSS Grid layout
- Remove Grid import since it's no longer used
- Fix Grid warnings: item, xs, sm, md props deprecated in MUI v7
- Use responsive CSS Grid with gridTemplateColumns for all layouts

Security improvements:
- Check authentication status on every page load
- Auto-redirect to login if no valid session exists
- Handle expired tokens gracefully without breaking logout flow

parentflow-admin/src/components/AdminLayout.tsx

@@ -1,6 +1,6 @@
 'use client';
 
-import { useState, ReactNode } from 'react';
+import { useState, useEffect, ReactNode } from 'react';
 import { useRouter, usePathname } from 'next/navigation';
 import {
   Box,
@@ -45,6 +45,13 @@ export default function AdminLayout({ children }: AdminLayoutProps) {
   const [mobileOpen, setMobileOpen] = useState(false);
   const [anchorEl, setAnchorEl] = useState<null | HTMLElement>(null);
 
+  // Check authentication on mount
+  useEffect(() => {
+    if (!apiClient.isAuthenticated()) {
+      router.push('/login');
+    }
+  }, [router]);
+
   const handleDrawerToggle = () => {
     setMobileOpen(!mobileOpen);
   };