perf: preload theme button and background images on app startup

src/lib/utils/preload-utils.ts

@@ -0,0 +1,21 @@
+import { THEME_BUTTON_IMAGES, THEME_BACKGROUND_IMAGES } from '../../generated/asset-manifest';
+
+/**
+ * Preloads an array of image URLs by creating Image objects.
+ * Images are loaded in the background and cached by the browser.
+ */
+const preloadImages = (imagePaths: readonly string[]): void => {
+  imagePaths.forEach((path) => {
+    const img = new Image();
+    img.src = `/${path}`;
+  });
+};
+
+/**
+ * Preloads all theme-related assets (buttons, backgrounds) on app startup.
+ * This prevents visible loading delays when switching themes.
+ */
+export const preloadThemeAssets = (): void => {
+  preloadImages(THEME_BUTTON_IMAGES);
+  preloadImages(THEME_BACKGROUND_IMAGES);
+};