- 新增 API 端点获取模型在各渠道的定价信息，支持全局价格回退
- 在模型详情侧边栏添加渠道价格卡片，显示所有支持该模型的渠道
- 优化 HorizontalFilterRow 组件，改用 flex-wrap 自动换行布局
- 隐藏数量为 0 的模型类型筛选项

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

Add a new /api/user/channels endpoint that returns only enabled channels
with non-sensitive fields (id, name, type, remark) for token channel binding.
Update EditTokenModal to use this endpoint and display remark instead of ID
in the channel dropdown.

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

Add new route groups for channel pricing and pricing tag management
with AdminAuth middleware.

Routes added:
- /api/channel_pricing/*: CRUD operations for channel pricing
- /api/pricing_tag/*: CRUD operations for pricing tags

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