fix: apply theme preference on login page

- Login component now applies saved theme preference on mount
- Theme preference correctly persists across logout/login in all modes
- Fixes issue where login page would revert to default theme after logout

frontend-modern/src/components/Login.tsx

@@ -1,5 +1,6 @@
 import { Component, createSignal, Show, onMount, lazy, Suspense } from 'solid-js';
 import { setBasicAuth } from '@/utils/apiClient';
+import { STORAGE_KEYS } from '@/constants';
 
 // Force include FirstRunSetup with lazy loading
 const FirstRunSetup = lazy(() => import('./FirstRunSetup').then(m => ({ default: m.FirstRunSetup })));
@@ -17,6 +18,14 @@ export const Login: Component<LoginProps> = (props) => {
   const [loadingAuth, setLoadingAuth] = createSignal(true);
   
   onMount(async () => {
+    // Apply saved theme preference
+    const savedTheme = localStorage.getItem(STORAGE_KEYS.DARK_MODE);
+    if (savedTheme === 'true') {
+      document.documentElement.classList.add('dark');
+    } else {
+      document.documentElement.classList.remove('dark');
+    }
+    
     console.log('[Login] Starting auth check...');
     try {
       const response = await fetch('/api/security/status');