feat(Sora): 直连生成并移除sora2api依赖

实现直连 Sora 客户端、媒体落地与清理策略\n更新网关与前端配置以支持 Sora 平台\n补齐单元测试与契约测试，新增 curl 测试脚本\n\n测试: go test ./... -tags=unit

backend/internal/handler/wire.go

@@ -26,7 +26,6 @@ func ProvideAdminHandlers(
 	subscriptionHandler *admin.SubscriptionHandler,
 	usageHandler *admin.UsageHandler,
 	userAttributeHandler *admin.UserAttributeHandler,
-	modelHandler *admin.ModelHandler,
 ) *AdminHandlers {
 	return &AdminHandlers{
 		Dashboard:        dashboardHandler,
@@ -46,7 +45,6 @@ func ProvideAdminHandlers(
 		Subscription:     subscriptionHandler,
 		Usage:            usageHandler,
 		UserAttribute:    userAttributeHandler,
-		Model:            modelHandler,
 	}
 }
 
@@ -121,7 +119,6 @@ var ProviderSet = wire.NewSet(
 	admin.NewSubscriptionHandler,
 	admin.NewUsageHandler,
 	admin.NewUserAttributeHandler,
-	admin.NewModelHandler,
 
 	// AdminHandlers and Handlers constructors
 	ProvideAdminHandlers,