📱 feat(TopUp): enhance mobile UX with responsive layout and bottom fixed payment panel

- Convert copy button to Input suffix for cleaner UI design
- Add responsive grid layout for balance cards and preset amounts
  - Mobile (< md): single column layout for better readability
  - Desktop (>= md): multi-column layout for space efficiency
- Implement bottom fixed payment panel on mobile devices
  - Fixed positioning for easy access to payment options
  - Includes custom amount input and payment method buttons
  - Auto-hide on desktop to maintain original layout
- Improve mobile payment flow with sticky bottom controls
- Add proper spacing to prevent content overlap with fixed elements
- Maintain consistent functionality across all breakpoints

This update significantly improves the mobile user experience by making
payment controls easily accessible without scrolling, while preserving
the desktop layout and functionality.

web/src/i18n/locales/en.json

@@ -971,6 +971,8 @@
   "最低": "lowest",
   "划转额度": "Transfer amount",
   "邀请链接": "Invitation link",
+  "划转邀请额度": "Transfer invitation quota",
+  "可用邀请额度": "Available invitation quota",
   "更多优惠": "More offers",
   "企业微信": "Enterprise WeChat",
   "点击解绑WxPusher": "Click to unbind WxPusher",