feat(user): 新增用户信息更新接口

新增 KeyboardUserReq DTO、Mapper updateByuid 方法及对应 XML，支持昵称/性别/头像/邮箱字段动态更新；补充 USER_INFO_UPDATE_FAILED 错误码，并在 UserController 与 UserServiceImpl 实现 updateUserInfo 逻辑。

src/main/resources/mapper/KeyboardUserMapper.xml

@@ -23,4 +23,15 @@
     id, "uid", nick_name, gender, avatar_url, created_at, updated_at, deleted, email, 
     "status", "password", subject_id, email_verified
   </sql>
+
+  <update id="updateByuid">
+        update keyboard_user
+        <set>
+            <if test="nickName != null">nick_name = #{nickName},</if>
+            <if test="gender != null">gender = #{gender},</if>
+            <if test="avatarUrl != null">avatar_url = #{avatarUrl},</if>
+            <if test="email != null">email = #{email},</if>
+        </set>
+        where uid = #{uid}
+    </update>
 </mapper>