feat(auth): 新增 Apple 登录并集成 Sa-Token 鉴权

- AppleServiceImpl：返回完整用户信息并签发 Sa-Token
- 新增 KeyboardUser 实体、Mapper、Service，支持按 subjectId 查询与创建
- GlobalExceptionHandler 统一处理 Sa-Token 未登录异常
- 补充 APPLE_LOGIN_ERROR 等错误码
- 配置文件增加 Sa-Token 相关参数

src/main/resources/application.yml

@@ -15,11 +15,6 @@ spring:
     name: keyborad-backend
   profiles:
     active: dev
-  datasource:
-    driver-class-name: org.postgresql.Driver
-    url: jdbc:postgresql://localhost:5432/keyborad_db
-    username: root
-    password: 123asd
   mvc:
     pathmatch:
       matching-strategy: ANT_PATH_MATCHER
@@ -44,7 +39,7 @@ server:
       enabled: true
 mybatis-plus:
   configuration:
-    map-underscore-to-camel-case: false
+    map-underscore-to-camel-case: true
     log-impl: org.apache.ibatis.logging.slf4j.Slf4jImpl
   global-config:
     db-config: