fix(groups): merge main and resolve model allowlist conflicts

Resolve three conflicts from main's #6680 (supplementUnmappedOpenAIModels):

1. gateway_handler.go — keep PR's allowlist refactoring (ModelAllowlistEnabled,
   writeAllowlistedModelsList, modelListingSource); main's OpenAI branch in
   writeModelsList was auto-merged.
2. group_models_list.go (modify/delete) — delete file per PR intent; relocate
   supplementUnmappedOpenAIModels to group_model_allowlist.go where gateway_service
   and openai_codex_models_service can still call it.
3. openai_codex_models_service.go — combine main's supplementUnmappedOpenAIModels
   wrapping with PR's ModelAllowlistEnabled() guard.

Also fix two auto-merged test files that still referenced the old
GroupModelsListConfig / ModelsListConfig types.

frontend/src/api/channels.ts

@@ -31,6 +31,10 @@ export interface UserPricingInterval {
   cache_write_price: number | null
   cache_write_1h_price?: number | null
   cache_read_price: number | null
+  input_multiplier?: number | null
+  output_multiplier?: number | null
+  cache_write_multiplier?: number | null
+  cache_read_multiplier?: number | null
   per_request_price: number | null
 }
 

frontend/src/api/modelPlaza.ts

@@ -46,7 +46,7 @@ export interface PlazaTimePricing {
 export interface PlazaModel {
   name: string
   platform: string
-  /** 实收口径的展示定价：多档时 intervals 为各档绝对单价（已由计费服务折算）；均为标准时段价。 */
+  /** 实收口径的展示定价：档位可提供绝对单价或相对基础价倍率；均为标准时段价。 */
   pricing: UserSupportedModelPricing | null
   official_pricing: PlazaOfficialPricing | null
   /** 仅多档模型返回。 */