feat(orderTrack): add contract functionality in goods detail component

- Introduced a new method for adding contracts in the goods detail component.
- Enhanced the existing contract download functionality to ensure proper handling of PDF files.
- Improved code clarity by adjusting variable declarations for better readability.

src/views/OrderTrack/goodsDetail.vue

@@ -410,6 +410,10 @@
                     });
                 }
             },
+            // 新增合同
+            addContract() {
+              
+            },
             //下载猎芯合同
             downloadContract() {
                 let pdf_url = ""
@@ -424,7 +428,7 @@
                 }
                 this.$http('get', pdf_url, { id: this.$route.query.purchase_id }, true, 'blob').then(res => {
                     // 包装成 Blob 对象
-                    const blob = new Blob([res], { type: 'application/pdf' });
+                    let blob = new Blob([res], { type: 'application/pdf' });
                     // 创建 URL 对象
                     let pdfUrl = window.URL.createObjectURL(blob);
                     window.open(pdfUrl, '_blank');