fix(billing): 默认开启 OpenAI 长上下文计费

backend/internal/handler/admin/account_codex_import.go

@@ -115,6 +115,10 @@ func (h *AccountHandler) ImportCodexSession(c *gin.Context) {
 		response.BadRequest(c, "Invalid request: "+err.Error())
 		return
 	}
+	if err := service.ValidateOpenAILongContextBillingExtra(service.PlatformOpenAI, req.Extra); err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
 	if req.Concurrency != nil && *req.Concurrency < 0 {
 		response.BadRequest(c, "concurrency must be >= 0")
 		return