feat(stocking): 添加备货单车辆明细行内附件上传

每辆车行增加「上传附件」按钮与文件标签列表，附件随车辆
提交（attachment 字段）。

Co-Authored-By: Claude <noreply@anthropic.com>

src/views/crmpc/stocking/Add.vue

@@ -194,6 +194,35 @@
                 <ElInput v-model="item.mileage" placeholder="请输入里程" />
               </ElFormItem>
             </ElCol>
+            <ElCol :sm="12" :md="12" :lg="6" :xl="4">
+              <ElFormItem label="附件" label-width="85px">
+                <el-upload
+                  :action="itemUploadAction"
+                  :headers="uploadHeaders"
+                  :show-file-list="false"
+                  :before-upload="beforeItemAttachmentUpload"
+                  :on-success="(res: any) => handleItemAttachmentUpload(res, idx)"
+                  multiple
+                  accept=".jpg,.jpeg,.png,.gif,.pdf,.doc,.docx,.xls,.xlsx,.txt"
+                >
+                  <el-button size="small" type="primary" plain>上传附件</el-button>
+                </el-upload>
+                <div
+                  v-if="item.attachment_files && item.attachment_files.length"
+                  style="margin-top: 4px"
+                >
+                  <el-tag
+                    v-for="(f, fIdx) in item.attachment_files"
+                    :key="fIdx"
+                    closable
+                    @close="removeItemAttachment(idx, fIdx)"
+                    style="margin: 2px 4px 2px 0"
+                  >
+                    {{ f.name }}
+                  </el-tag>
+                </div>
+              </ElFormItem>
+            </ElCol>
           </ElRow>
           <ElRow :gutter="12" class="item-row-wrap">
             <ElCol :sm="12" :md="12" :lg="6" :xl="4" v-if="(item.mileage ?? 0) <= 0">
@@ -1207,7 +1236,14 @@
     getVehicleList,
     handleVehicleSizeChange,
     handleVehicleCurrentChange,
-    chooseVehicle
+    chooseVehicle,
+
+    // 车辆附件上传
+    uploadHeaders,
+    itemUploadAction,
+    beforeItemAttachmentUpload,
+    handleItemAttachmentUpload,
+    removeItemAttachment
   } = useStockingForm(false) // isFinal = false
 
   // ---------- 草稿缓存：保存/恢复/清理 ----------