fix(outbound): 出库备注改为必填，按单出库自动填充申请原因

- 备注字段新增 required 校验规则
- placeholder 从「可选填」改为「请填写出库原因」
- 按单出库模式选择申请单后，自动将申请原因填入备注

inventory-web/src/views/outbound/create.vue

@@ -197,8 +197,8 @@
             </el-col>
           </el-row>
 
-          <el-form-item label="备注说明" prop="remark">
-            <el-input v-model="form.remark" type="textarea" :rows="2" placeholder="可选填" />
+          <el-form-item label="备注说明" prop="remark" required>
+            <el-input v-model="form.remark" type="textarea" :rows="2" placeholder="请填写出库原因" />
           </el-form-item>
 
           <el-form-item label="电子签名确认" required>
@@ -332,7 +332,8 @@ const form = reactive({
 const rules = {
   outbound_type: [{ required: true, message: '请选择出库类型', trigger: 'change' }],
   consumer_name: [{ required: true, message: '请输入领用人姓名', trigger: 'blur' }],
-  operator_name: [{ required: true, message: '请指定操作员', trigger: 'change' }]
+  operator_name: [{ required: true, message: '请指定操作员', trigger: 'change' }],
+  remark: [{ required: true, message: '请填写备注/出库原因', trigger: 'blur' }]
 }
 
 // 计算总金额
@@ -382,8 +383,13 @@ const loadApprovalRequests = async () => {
 const handleRequestChange = (val: number | null) => {
   if (!val) {
     selectedRequest.value = null
+    form.remark = ''
   } else {
     selectedRequest.value = approvalRequests.value.find(r => r.id === val) ?? null
+    // ★ 按单出库：自动将申请单的申请原因填入备注，用户可修改
+    if (selectedRequest.value?.remark) {
+      form.remark = selectedRequest.value.remark
+    }
   }
   // 切换申请单时清空购物车，防止已扫物品与新单据混淆
   cartItems.value = []