fix: unify theme system - fix theme switching persistence

- Unified localStorage key to 'theme-preference' across all components
- Fixed header.tsx using wrong localStorage key ('theme' instead of 'theme-preference')
- Added localStorage hybrid persistence for instant theme changes
- Removed router.refresh() which was causing stale data revert
- Replaced Blue theme with Sepia
- Consolidated auth() calls to prevent race conditions
- Updated UserSettingsData types to include all themes

keep-notes/app/(main)/admin/settings/page.tsx

@@ -1,21 +1,23 @@
-import { auth } from '@/auth'
-import { redirect } from 'next/navigation'
 import { getSystemConfig } from '@/app/actions/admin-settings'
 import { AdminSettingsForm } from './admin-settings-form'
 
 export default async function AdminSettingsPage() {
-  const session = await auth()
-  
-  if ((session?.user as any)?.role !== 'ADMIN') {
-    redirect('/')
-  }
-
   const config = await getSystemConfig()
 
   return (
-    <div className="container max-w-4xl mx-auto py-10 px-4">
-      <h1 className="text-3xl font-bold mb-8">System Configuration</h1>
-      <AdminSettingsForm config={config} />
+    <div className="space-y-6">
+      <div>
+        <h1 className="text-3xl font-bold text-gray-900 dark:text-white">
+          Settings
+        </h1>
+        <p className="text-gray-600 dark:text-gray-400 mt-1">
+          Configure application-wide settings
+        </p>
+      </div>
+
+      <div className="bg-white dark:bg-zinc-900 rounded-lg shadow overflow-hidden border border-gray-200 dark:border-gray-800 p-6">
+        <AdminSettingsForm config={config} />
+      </div>
     </div>
   )
 }