fix(ui): improve background handling and PWA update prompts

- Add adaptive solid color background support for dark/light themes.
- Replace mesh gradient with semi-transparent blurred background images.
- Fix background scrolling issue on mobile browsers.
- Remove borders from specific cards for consistent UI styling.
- Prevent caching of PWA service worker files in Nginx.
- Introduce interactive toast prompt for PWA updates instead of silent refresh.

vite-frontend/vite.config.ts

@@ -8,7 +8,7 @@ export default defineConfig({
   plugins: [
     react(),
     VitePWA({
-      registerType: "autoUpdate",
+      registerType: "prompt",
       injectRegister: "auto",
       includeAssets: ["favicon.ico", "apple-touch-icon.png"],
       manifest: {