fix: 报名时强制验证联系人是否已选择

- 在goToStep3方法中添加selectedContact验证
- 未选择联系人时显示提示并阻止提交
- 修复Issue #2

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

src/pages/event-register/event-register.vue

@@ -589,6 +589,12 @@ export default {
           return
         }
 
+        // 强制验证联系人是否已选择
+        if (!this.selectedContact) {
+          uni.showToast({ title: '请选择联系人', icon: 'none' })
+          return
+        }
+
         const now = new Date()
         const orderNo = `BM${now.getFullYear()}${String(now.getMonth() + 1).padStart(2, '0')}${String(now.getDate()).padStart(2, '0')}${String(now.getHours()).padStart(2, '0')}${String(now.getMinutes()).padStart(2, '0')}${String(now.getSeconds()).padStart(2, '0')}${String(Math.floor(Math.random() * 10000)).padStart(4, '0')}`