支付宝支付：
- 后端：新增 topup_alipay.go、payment_alipay.go，实现当面付（扫码支付）下单、
  回调验签、订单状态查询完整流程，支持 RSA2 签名
- 前端：新增 QRCodePayModal 通用二维码支付弹窗（泛化微信支付弹窗）、
  SettingsPaymentGatewayAlipay 管理配置页面、充值流程接入支付宝
- 充值历史：管理员视图新增用户邮箱列，后端 fillTopUpEmails 批量填充

i18n 补全：
- 54 个缺失翻译 key 添加到全部 7 个 locale 文件（zh-CN/zh-TW/en/fr/ja/ru/vi）
- 涵盖渠道名称、仪表盘标签、兑换码状态、控制台时间筛选、Playground 错误消息、
  Dashboard 设置页面提示等
- 14 个源码文件中约 31 处 showError/showSuccess/showWarning 硬编码中文改用 t()
- ChannelsColumnDefs、helpers、services 中散落的硬编码中文统一国际化

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

- Add "by price" sub-mode for per-token pricing (auto-calculate ratios)
- Add color picker with preset colors in tag manager
- Display tags with colors in channel pricing view and selector
- Remove unused function, extract hardcoded color constants
- Fix pricing model filter (status==0 instead of status!=1)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

- Add view mode switch (global vs channel) to ModelSettingsVisualEditor
- Create ChannelPricingView component for channel-specific pricing
- Add pricing tag management tab to RatioSetting

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>