docs(api): 更新计划书API文档，年龄与出生年月日改为二选一

- customer_age 和 customer_birthday 不再是必填字段
- 改为条件必填：至少提供一个即可
- 添加字段描述说明

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

@@ -52,9 +52,12 @@ paths:
                 customer_age:
                 customer_age:
                   type: integer
                   type: integer
                   title: 年龄
                   title: 年龄
+                  description: 与 customer_birthday 二选一，至少提供一个
                 customer_birthday:
                 customer_birthday:
                   type: string
                   type: string
                   title: 出生年月日
                   title: 出生年月日
+                  format: date
+                  description: 与 customer_age 二选一，至少提供一个。格式：YYYY-MM-DD
                 annual_premium:
                 annual_premium:
                   type: integer
                   type: integer
                   title: 保额
                   title: 保额
@@ -94,8 +97,9 @@ paths:
               required:
               required:
                 - customer_name
                 - customer_name
                 - customer_gender
                 - customer_gender
-                - customer_age
-                - customer_birthday
+                # 年龄与出生年月日二选一（至少提供一个）
+                # - customer_age
+                # - customer_birthday
                 - annual_premium
                 - annual_premium
                 - payment_years
                 - payment_years
                 - currency_type
                 - currency_type