[rewrite] Added shadcn ui to frontend and slightly tweaked backend

frontend/src/features/settings/appearance/index.tsx

@@ -0,0 +1,14 @@
+import ContentSection from '../components/content-section'
+import { AppearanceForm } from './appearance-form'
+
+export default function SettingsAppearance() {
+  return (
+    <ContentSection
+      title='Appearance'
+      desc='Customize the appearance of the app. Automatically switch between day
+          and night themes.'
+    >
+      <AppearanceForm />
+    </ContentSection>
+  )
+}