feat(user-relation): 实现用户关注与取消关注功能

- 在 t_following 和 t_fans 表中添加联合唯一索引，确保关注关系的幂等性- 新增 RocketMQ 消费者 FollowUnfollowConsumer，处理关注和取消关注消息
- 实现关注逻辑，通过事务保证关注表和粉丝表数据一致性
- 修改 DeleteNoteLocalCacheConsumer 的 consumerGroup 名称，避免消费者组冲突，否则可能遇到消费者不消费的情况

han-note-user-relation/han-note-user-relation-biz/src/main/java/com/hanserwei/hannote/user/relation/biz/consumer/FollowUnfollowConsumer.java

@@ -0,0 +1,102 @@
+package com.hanserwei.hannote.user.relation.biz.consumer;
+
+import com.hanserwei.framework.common.utils.JsonUtils;
+import com.hanserwei.hannote.user.relation.biz.constant.MQConstants;
+import com.hanserwei.hannote.user.relation.biz.domain.dataobject.FansDO;
+import com.hanserwei.hannote.user.relation.biz.domain.dataobject.FollowingDO;
+import com.hanserwei.hannote.user.relation.biz.model.dto.FollowUserMqDTO;
+import com.hanserwei.hannote.user.relation.biz.service.FansDOService;
+import com.hanserwei.hannote.user.relation.biz.service.FollowingDOService;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.rocketmq.common.message.Message;
+import org.apache.rocketmq.spring.annotation.RocketMQMessageListener;
+import org.apache.rocketmq.spring.core.RocketMQListener;
+import org.springframework.stereotype.Component;
+import org.springframework.transaction.support.TransactionTemplate;
+
+import java.time.LocalDateTime;
+import java.util.Objects;
+
+@Component
+@RocketMQMessageListener(
+        consumerGroup = "han_note_group_" + MQConstants.TOPIC_FOLLOW_OR_UNFOLLOW,
+        topic = MQConstants.TOPIC_FOLLOW_OR_UNFOLLOW
+)
+@Slf4j
+public class FollowUnfollowConsumer implements RocketMQListener<Message> {
+    private final TransactionTemplate transactionTemplate;
+    private final FollowingDOService followingDOService;
+    private final FansDOService fansDOService;
+
+    public FollowUnfollowConsumer(TransactionTemplate transactionTemplate, FollowingDOService followingDOService, FansDOService fansDOService) {
+        this.transactionTemplate = transactionTemplate;
+        this.followingDOService = followingDOService;
+        this.fansDOService = fansDOService;
+    }
+
+    @Override
+    public void onMessage(Message message) {
+        // 消息体
+        String bodyJsonStr = new String(message.getBody());
+        // 标签
+        String tags = message.getTags();
+
+        log.info("==> FollowUnfollowConsumer 消费了消息 {}, tags: {}", bodyJsonStr, tags);
+        // 根据MQ标签判断操作类型
+        if (Objects.equals(tags, MQConstants.TAG_FOLLOW)){
+            // 关注
+            handleFollowTagMessage(bodyJsonStr);
+        } else if (Objects.equals(tags, MQConstants.TAG_UNFOLLOW)) {
+            // 取关
+            // TODO: 待实现
+        }
+    }
+
+    /**
+     * 关注
+     * @param bodyJsonStr 消息体
+     */
+    private void handleFollowTagMessage(String bodyJsonStr) {
+        // 解析消息体转换为DTO对象
+        FollowUserMqDTO followUserMqDTO = JsonUtils.parseObject(bodyJsonStr, FollowUserMqDTO.class);
+
+        // 判空
+        if (Objects.isNull(followUserMqDTO)) {
+            return;
+        }
+
+        // 幂等性：通过联合唯一索引保证
+
+        Long userId = followUserMqDTO.getUserId();
+        Long followUserId = followUserMqDTO.getFollowUserId();
+        LocalDateTime createTime = followUserMqDTO.getCreateTime();
+
+        // 编程式事物
+        boolean isSuccess = Boolean.TRUE.equals(transactionTemplate.execute(status -> {
+            try {
+                // 关注成功需往数据库添加两条记录
+                // 关注表：一条记录
+                boolean followRecordSaved = followingDOService.save(FollowingDO.builder()
+                        .userId(userId)
+                        .followingUserId(followUserId)
+                        .createTime(createTime)
+                        .build());
+                // 粉丝表：一条记录
+                if (followRecordSaved){
+                    return fansDOService.save(FansDO.builder()
+                            .userId(followUserId)
+                            .fansUserId(userId)
+                            .createTime(createTime)
+                            .build());
+                }
+            }catch (Exception e){
+                status.setRollbackOnly();
+                log.error("## 添加关注关系失败, userId: {}, followUserId: {}, createTime: {}", userId, followUserId, createTime);
+            }
+            return false;
+        }));
+
+        log.info("## 数据库添加记录结果: {}", isSuccess);
+        // TODO: 更新 Redis 中被关注用户的 ZSet 粉丝列表
+    }
+}