feat(channel): 渠道管理全链路集成 — 模型映射、定价、限制、用量统计

- 渠道模型映射：支持精确匹配和通配符映射，按平台隔离
- 渠道模型定价：支持 token/按次/图片三种计费模式，区间分层定价
- 模型限制：渠道可限制仅允许定价列表中的模型
- 计费模型来源：支持 requested/upstream 两种计费模型选择
- 用量统计：usage_logs 新增 channel_id/model_mapping_chain/billing_tier/billing_mode 字段
- Dashboard 支持 model_source 维度（requested/upstream/mapping）查看模型统计
- 全部 gateway handler 统一接入 ResolveChannelMappingAndRestrict
- 修复测试：同步 SoraGenerationRepository 接口、SQL INSERT 参数、scan 字段

frontend/src/i18n/locales/en.ts

@@ -1744,6 +1744,8 @@ export default {
       deleteError: 'Failed to delete channel',
       nameRequired: 'Please enter a channel name',
       duplicateModels: 'Model "{0}" appears in multiple pricing entries',
+      modelConflict: "Model patterns '{model1}' and '{model2}' conflict: overlapping match range",
+      mappingConflict: "Mapping source patterns '{model1}' and '{model2}' conflict: overlapping match range",
       deleteConfirm: 'Are you sure you want to delete channel "{name}"? This cannot be undone.',
       columns: {
         name: 'Name',