feat(plan): 添加提取方式字段映射

- 在提交数据映射中添加 withdrawal_method 字段
- 确保提取方式正确提交到后端

影响文件:
- src/components/plan/PlanFormContainer.vue

@@ -279,8 +279,9 @@ const submit = async () => {
       withdrawal_period: 'withdrawal_period',       // 提取期
       currency_type: 'currency_type',        // 币种类型
       // 新增字段映射
+      withdrawal_method: 'withdrawal_method',       // 提取方式
       annual_withdrawal_amount: 'annual_withdrawal_amount',        // 每年提取金额
-      annual_increase_percentage: 'annual_increase_percentage'       // 每年递增提取百分比
+      annual_increase_percentage: 'annual_increase_percentage',       // 每年递增提取百分比
     }
 
     // 构建请求数据