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/nginx.conf

@@ -43,6 +43,14 @@ http {
         root /usr/share/nginx/html;
         index index.html;
 
+        # PWA 和 Service Worker 不缓存
+        location ~* (sw\.js|service-worker\.js|workbox-.*\.js|manifest\.webmanifest)$ {
+            add_header Cache-Control "no-cache, no-store, must-revalidate";
+            add_header Pragma "no-cache";
+            add_header Expires "0";
+            try_files $uri =404;
+        }
+
         # 静态文件缓存
         location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg)$ {
             expires 30d;