refactor(channels): tighten types and error paths per second review

- service: drop groupRepo nil guard (DI must inject), switch SupportedModels to SliceStable to match doc
- frontend: reuse user-side DTO types in SupportedModelChip/AvailableChannelsTable instead of duplicating shapes; narrow admin statusLabel param to ChannelStatus
- tests: replace nil-groupRepo case with ListAll/ListActive error propagation and BillingModelSource default-backfill coverage

frontend/src/components/channels/AvailableChannelsTable.vue

@@ -61,6 +61,7 @@ import { computed, useSlots } from 'vue'
 import DataTable from '@/components/common/DataTable.vue'
 import Icon from '@/components/icons/Icon.vue'
 import SupportedModelChip from './SupportedModelChip.vue'
+import type { UserSupportedModelPricing } from '@/api/channels'
 
 interface GroupRef {
   id: number
@@ -75,7 +76,7 @@ interface Row {
   supported_models: Array<{
     name: string
     platform: string
-    pricing: unknown | null
+    pricing: UserSupportedModelPricing | null
   }>
   [key: string]: unknown
 }

frontend/src/components/channels/SupportedModelChip.vue

@@ -127,34 +127,15 @@ import {
   BILLING_MODE_IMAGE,
   type BillingMode
 } from '@/constants/channel'
+import type { UserPricingInterval, UserSupportedModel } from '@/api/channels'
 
-interface PricingInterval {
-  min_tokens: number
-  max_tokens: number | null
-  tier_label?: string
-  input_price: number | null
-  output_price: number | null
-  cache_write_price: number | null
-  cache_read_price: number | null
-  per_request_price: number | null
-}
-
-interface SupportedModelPricing {
-  billing_mode: BillingMode
-  input_price: number | null
-  output_price: number | null
-  cache_write_price: number | null
-  cache_read_price: number | null
-  image_output_price: number | null
-  per_request_price: number | null
-  intervals: PricingInterval[]
-}
-
-interface SupportedModelLike {
-  name: string
-  platform: string
-  pricing: SupportedModelPricing | null
-}
+/**
+ * 复用 api/channels.ts 的用户侧最小形态 DTO。
+ * admin 侧 ChannelModelPricing 字段更多，但结构上是用户 DTO 的超集，
+ * 因此 admin 视图传入时 TypeScript 结构化子类型会直接通过。
+ */
+type PricingInterval = UserPricingInterval
+type SupportedModelLike = UserSupportedModel
 
 const props = withDefaults(
   defineProps<{

frontend/src/views/admin/AvailableChannelsView.vue

@@ -78,7 +78,7 @@ import AvailableChannelsTable from '@/components/channels/AvailableChannelsTable
 import channelsAPI, { type AvailableChannel } from '@/api/admin/channels'
 import { useAppStore } from '@/stores/app'
 import { extractApiErrorMessage } from '@/utils/apiError'
-import { CHANNEL_STATUS_ACTIVE } from '@/constants/channel'
+import { CHANNEL_STATUS_ACTIVE, type ChannelStatus } from '@/constants/channel'
 
 const { t } = useI18n()
 const appStore = useAppStore()
@@ -95,7 +95,7 @@ const columns = computed(() => [
   { key: 'supported_models', label: t('admin.availableChannels.columns.supportedModels') }
 ])
 
-function statusLabel(status: string): string {
+function statusLabel(status: ChannelStatus): string {
   return status === CHANNEL_STATUS_ACTIVE
     ? t('admin.availableChannels.statusActive')
     : t('admin.availableChannels.statusDisabled')