feat: standardize UI theme, fix dark mode consistency, and implement editorial tags

memento-note/app/(main)/layout.tsx

@@ -31,12 +31,12 @@ export default async function MainLayout({
   return (
     <ProvidersWrapper initialLanguage={initialLanguage} initialTranslations={initialTranslations}>
       {/* No top-bar header — sidebar-only navigation (architectural-grid design) */}
-      <div className="flex h-screen overflow-hidden bg-memento-desk">
+      <div className="flex h-screen overflow-hidden bg-memento-desk dark:bg-background">
         <Suspense fallback={<div className="hidden w-80 shrink-0 md:block" />}>
           <Sidebar user={session?.user} />
         </Suspense>
 
-        <main className="flex min-h-0 flex-1 flex-col overflow-y-auto scroll-smooth bg-memento-paper">
+        <main className="flex min-h-0 flex-1 flex-col overflow-y-auto scroll-smooth bg-memento-paper dark:bg-background">
           {children}
         </main>