删除用户渠道倍率（UserChannelRatio）功能，清理全链路相关代码：
后端删除 model/controller/router 层实现，前端删除 UI 组件和计费展示逻辑。
同时恢复 Token 分组选择和价格侧边栏分组过滤器的注释代码。

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

Add unit tests for group ratio, cross-group retry, and price calculation:
- Group ratio CRUD and special ratio override (12 tests)
- HandleGroupRatio with auto-group and special ratios (5 tests)
- ModelPriceHelper with group ratio in price/ratio modes (3 tests)
- Channel selection priority, groups, weighted LB (6 tests)
- RetryParam and AutoGroup service logic (7 tests)

Also restore the group pricing card in model detail SideSheet.

Delete leftover channel pricing controllers and routes after removing channel pricing, and align relay price helpers with global pricing plus user channel ratio only.

Co-Authored-By: Codex <noreply@anthropic.com>

使用注释方式隐藏分组列和分组倍率标签，便于后续恢复：
1. 注释 UsageLogsColumnDefs.jsx 中的分组列定义
2. 注释 useUsageLogsData.jsx 中的 COLUMN_KEYS.GROUP 和默认可见性配置
3. 将计费详情中的"分组倍率"改为"倍率"

后端计费逻辑不变，仍正常应用分组倍率。

Co-Authored-By: Claude Sonnet 4 <noreply@anthropic.com>