feat: configure responsive image sizes for optimized loading

- Added custom deviceSizes configuration in next.config.ts to support common mobile and desktop breakpoints
- Added responsive sizes attribute to hall wallet strip background image for proper srcset generation

next.config.ts

@@ -9,6 +9,10 @@ const nextConfig: NextConfig = {
   ...(allowedDevOrigins.length > 0 ? { allowedDevOrigins } : {}),
   reactCompiler: true,
 
+  images: {
+    deviceSizes: [640, 750, 828, 1080, 1200, 1920],
+  },
+
   // 非 CSP 安全头；CSP 由 middleware 按后台接入站点白名单动态生成。
   async headers() {
     return [