feat: update theme management across the application; change default theme to 'light', disable system theme option, and add ThemeCard component in settings for enhanced user customization

components/settings/index.ts

@@ -5,3 +5,4 @@ export { BackupCard } from "./backup-card";
 export { PasswordCard } from "./password-card";
 export { ReconcileDateRangeCard } from "./reconcile-date-range-card";
 export { BackgroundCard } from "./background-card";
+export { ThemeCard } from "./theme-card";