fix(apply): 优化表单验证逻辑以提高可读性和维护性

重构 validateForm 方法，使用规则数组简化验证逻辑，减少重复代码。

pages/apply/index.vue

@@ -166,42 +166,23 @@
              */
             validateForm() {
                 var { apply_type, order_sn, customer_name, apply_fee_amount, relief_detail, relief_reason } = this.form;
-                
-                if (!apply_type) {
-                    this.errorMsg = '请选择申请类型';
-                    return false;
-                }
-                
-                if (!order_sn) {
-                    this.errorMsg = '请输入订单号';
-                    return false;
-                }
 
-                if (!apply_fee_amount) {
-                    this.errorMsg = '请输入申请免收金额';
-                    return false;
-                }
-                
-                if (isNaN(apply_fee_amount) || Number(apply_fee_amount) <= 0) {
-                    this.errorMsg = '请输入有效的申请免收金额';
-                    return false;
-                }
-                
-                if (!relief_detail) {
-                    this.errorMsg = '请选择减免明细';
-                    return false;
-                }
-                
-                if (!relief_reason) {
-                    this.errorMsg = '请输入免收原因';
+                var rules = [
+                    { invalid: !apply_type, msg: '请选择申请类型' },
+                    { invalid: !order_sn, msg: '请输入订单号' },
+                    { invalid: !apply_fee_amount, msg: '请输入申请免收金额' },
+                    { invalid: isNaN(apply_fee_amount) || Number(apply_fee_amount) <= 0, msg: '请输入有效的申请免收金额' },
+                    { invalid: !relief_detail, msg: '请选择减免明细' },
+                    { invalid: !relief_reason, msg: '请输入免收原因' },
+                    { invalid: !customer_name, msg: '请输入有效的订单号以获取客户名称' }
+                ];
+
+                var failedRule = rules.find(rule => rule.invalid);
+                if (failedRule) {
+                    this.errorMsg = failedRule.msg;
                     return false;
                 }
 
-                if (!customer_name) {
-                    this.errorMsg = '请输入有效的订单号以获取客户名称';
-                    return false;
-                }
-                
                 this.errorMsg = '';
                 return true;
             },