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/mapper/KeyboardUserMapper.xml

@@ -0,0 +1,26 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
+<mapper namespace="com.yolo.keyborad.mapper.KeyboardUserMapper">
+  <resultMap id="BaseResultMap" type="com.yolo.keyborad.model.entity.KeyboardUser">
+    <!--@mbg.generated-->
+    <!--@Table keyboard_user-->
+    <id column="id" jdbcType="BIGINT" property="id" />
+    <result column="uid" jdbcType="BIGINT" property="uid" />
+    <result column="nick_name" jdbcType="VARCHAR" property="nickName" />
+    <result column="gender" jdbcType="INTEGER" property="gender" />
+    <result column="avatar_url" jdbcType="VARCHAR" property="avatarUrl" />
+    <result column="created_at" jdbcType="TIMESTAMP" property="createdAt" />
+    <result column="updated_at" jdbcType="TIMESTAMP" property="updatedAt" />
+    <result column="deleted" jdbcType="BOOLEAN" property="deleted" />
+    <result column="email" jdbcType="VARCHAR" property="email" />
+    <result column="status" jdbcType="BOOLEAN" property="status" />
+    <result column="password" jdbcType="VARCHAR" property="password" />
+    <result column="subject_id" jdbcType="VARCHAR" property="subjectId" />
+    <result column="email_verified" jdbcType="BOOLEAN" property="emailVerified" />
+  </resultMap>
+  <sql id="Base_Column_List">
+    <!--@mbg.generated-->
+    id, "uid", nick_name, gender, avatar_url, created_at, updated_at, deleted, email, 
+    "status", "password", subject_id, email_verified
+  </sql>
+</mapper>