feat(billing): support safe upstream response model billing

frontend/src/constants/channel.ts

@@ -16,7 +16,9 @@ export type BillingMode =
 export const BILLING_MODEL_SOURCE_REQUESTED = 'requested' as const
 export const BILLING_MODEL_SOURCE_UPSTREAM = 'upstream' as const
 export const BILLING_MODEL_SOURCE_CHANNEL_MAPPED = 'channel_mapped' as const
+export const BILLING_MODEL_SOURCE_RESPONSE = 'response_model' as const
 export type BillingModelSource =
   | typeof BILLING_MODEL_SOURCE_REQUESTED
   | typeof BILLING_MODEL_SOURCE_UPSTREAM
   | typeof BILLING_MODEL_SOURCE_CHANNEL_MAPPED
+  | typeof BILLING_MODEL_SOURCE_RESPONSE

frontend/src/i18n/locales/en/admin/channels.ts

@@ -143,6 +143,7 @@ export default {
         billingModelSourceChannelMapped: 'Bill by channel-mapped model',
         billingModelSourceRequested: 'Bill by requested model',
         billingModelSourceUpstream: 'Bill by final upstream model',
+        billingModelSourceResponse: 'Bill by upstream response model',
         billingModelSourceHint: 'Controls which model name is used for pricing lookup',
         selectedCount: '{count} selected',
         searchGroups: 'Search groups...',

frontend/src/i18n/locales/zh/admin/channels.ts

@@ -143,6 +143,7 @@ export default {
         billingModelSourceChannelMapped: '以渠道映射后的模型计费',
         billingModelSourceRequested: '以请求模型计费',
         billingModelSourceUpstream: '以最终模型计费',
+        billingModelSourceResponse: '按上游响应模型计费',
         billingModelSourceHint: '控制使用哪个模型名称进行定价查找',
         selectedCount: '已选 {count} 个',
         searchGroups: '搜索分组...',

frontend/src/views/admin/ChannelsView.vue

@@ -713,7 +713,8 @@ const statusEditOptions = computed(() => [
 const billingModelSourceOptions = computed(() => [
   { value: 'channel_mapped', label: t('admin.channels.form.billingModelSourceChannelMapped', 'Bill by channel-mapped model') },
   { value: 'requested', label: t('admin.channels.form.billingModelSourceRequested', 'Bill by requested model') },
-  { value: 'upstream', label: t('admin.channels.form.billingModelSourceUpstream', 'Bill by final upstream model') }
+  { value: 'upstream', label: t('admin.channels.form.billingModelSourceUpstream', 'Bill by final upstream model') },
+  { value: 'response_model', label: t('admin.channels.form.billingModelSourceResponse', 'Bill by upstream response model') }
 ])
 
 // ── State ──