feat(chat): implement sequence-based unread count tracking

Introduce a new mechanism for tracking read positions using message
sequences (hasReadSeq), similar to OpenIM, to allow for O(1) unread
count calculations.

- Implement `UserReadSeq` caching in Redis with Lua scripts to prevent
  sequence regression (ensuring updates only occur if the new sequence
  is greater than the current one).
- Update `ConversationCache` to support sequence-based unread count
  computation (`maxSeq - hasReadSeq`).
- Refactor `MessageRepository` to use conditional updates for
  `last_read_seq` in the database.
- Update `ChatService` to automatically update the sender's read
  sequence when sending a message.
- Optimize `MarkAsRead` logic to update both database and Redis
  sequence caches and refine notification targets for private vs
  group chats.
- Update `jpush` client to use pointer types for boolean fields to
  properly handle optional values in JSON.

internal/cache/conversation_cache.go

@@ -484,6 +484,172 @@ func (c *ConversationCache) InvalidateUnreadCount(userID, convID string) {
 	c.cache.Delete(UnreadDetailKey(userID, convID))
 }
 
+// ============================================================
+// 已读位置缓存（OpenIM 风格 hasReadSeq）
+// ============================================================
+
+// readSeqExpire 已读位置缓存 TTL
+const readSeqExpire = 30 * 24 * time.Hour
+
+// SetUserReadSeq 设置用户在某会话的已读位置（防回退：仅当新值大于当前值时更新）
+func (c *ConversationCache) SetUserReadSeq(ctx context.Context, convID, userID string, seq int64) error {
+	key := UserReadSeqKey(convID, userID)
+
+	redisCache, ok := c.cache.(*RedisCache)
+	if !ok {
+		// 非 Redis 模式，直接设置
+		c.cache.Set(key, seq, readSeqExpire)
+		return nil
+	}
+
+	rdb := redisCache.GetRedisClient().GetClient()
+	nKey := normalizeKey(key)
+	// Lua 脚本：仅当新 seq > 当前值时才更新，防回退
+	script := redis.NewScript(`
+		local current = tonumber(redis.call('GET', KEYS[1]))
+		if current and current >= tonumber(ARGV[1]) then
+			return 0
+		end
+		redis.call('SET', KEYS[1], ARGV[1])
+		redis.call('EXPIRE', KEYS[1], ARGV[2])
+		return 1
+	`)
+	_, err := script.Run(ctx, rdb, []string{nKey}, seq, int64(readSeqExpire.Seconds())).Result()
+	return err
+}
+
+// GetUserReadSeq 获取用户在某会话的已读位置
+func (c *ConversationCache) GetUserReadSeq(ctx context.Context, convID, userID string) (int64, error) {
+	key := UserReadSeqKey(convID, userID)
+
+	redisCache, ok := c.cache.(*RedisCache)
+	if !ok {
+		raw, ok := c.cache.Get(key)
+		if !ok {
+			return 0, ErrKeyNotFound
+		}
+		switch v := raw.(type) {
+		case int64:
+			return v, nil
+		case string:
+			var n int64
+			fmt.Sscanf(v, "%d", &n)
+			return n, nil
+		}
+		return 0, ErrKeyNotFound
+	}
+
+	rdb := redisCache.GetRedisClient().GetClient()
+	nKey := normalizeKey(key)
+	val, err := rdb.Get(ctx, nKey).Int64()
+	if err != nil {
+		return 0, ErrKeyNotFound
+	}
+	return val, nil
+}
+
+// GetUserReadSeqs 批量获取用户在多个会话的已读位置
+func (c *ConversationCache) GetUserReadSeqs(ctx context.Context, userID string, convIDs []string) (map[string]int64, error) {
+	if len(convIDs) == 0 {
+		return nil, nil
+	}
+
+	redisCache, ok := c.cache.(*RedisCache)
+	if !ok {
+		result := make(map[string]int64, len(convIDs))
+		for _, convID := range convIDs {
+			if seq, err := c.GetUserReadSeq(ctx, convID, userID); err == nil {
+				result[convID] = seq
+			}
+		}
+		return result, nil
+	}
+
+	rdb := redisCache.GetRedisClient().GetClient()
+	keys := make([]string, len(convIDs))
+	for i, convID := range convIDs {
+		keys[i] = normalizeKey(UserReadSeqKey(convID, userID))
+	}
+
+	vals, err := rdb.MGet(ctx, keys...).Result()
+	if err != nil {
+		return nil, err
+	}
+
+	result := make(map[string]int64, len(convIDs))
+	for i, val := range vals {
+		if val == nil {
+			continue
+		}
+		var seq int64
+		fmt.Sscanf(fmt.Sprint(val), "%d", &seq)
+		result[convIDs[i]] = seq
+	}
+	return result, nil
+}
+
+// GetConvMaxSeq 获取会话的最大 seq（复用 msg_seq 计数器，读取当前值）
+func (c *ConversationCache) GetConvMaxSeq(ctx context.Context, convID string) (int64, error) {
+	seqKey := MessageSeqKey(convID)
+
+	redisCache, ok := c.cache.(*RedisCache)
+	if !ok {
+		return 0, ErrKeyNotFound
+	}
+
+	rdb := redisCache.GetRedisClient().GetClient()
+	nKey := normalizeKey(seqKey)
+	val, err := rdb.Get(ctx, nKey).Int64()
+	if err != nil {
+		return 0, ErrKeyNotFound
+	}
+	return val, nil
+}
+
+// ComputeUnreadCount 计算单个会话未读数：maxSeq - hasReadSeq
+func (c *ConversationCache) ComputeUnreadCount(ctx context.Context, convID, userID string) (int64, error) {
+	maxSeq, err := c.GetConvMaxSeq(ctx, convID)
+	if err != nil {
+		return 0, err
+	}
+	readSeq, err := c.GetUserReadSeq(ctx, convID, userID)
+	if err != nil {
+		// 未读到已读位置，视为 0，返回 maxSeq
+		return maxSeq, nil
+	}
+	unread := maxSeq - readSeq
+	if unread < 0 {
+		return 0, nil
+	}
+	return unread, nil
+}
+
+// ComputeAllUnreadCount 计算所有会话未读总数：sum(maxSeq - hasReadSeq)
+func (c *ConversationCache) ComputeAllUnreadCount(ctx context.Context, userID string, convIDs []string, maxSeqs map[string]int64) (int64, error) {
+	readSeqs, err := c.GetUserReadSeqs(ctx, userID, convIDs)
+	if err != nil {
+		return 0, err
+	}
+
+	var total int64
+	for _, convID := range convIDs {
+		maxSeq, ok := maxSeqs[convID]
+		if !ok {
+			continue
+		}
+		readSeq, hasRead := readSeqs[convID]
+		if !hasRead {
+			total += maxSeq
+			continue
+		}
+		unread := maxSeq - readSeq
+		if unread > 0 {
+			total += unread
+		}
+	}
+	return total, nil
+}
+
 // IncrementUnread 递增用户在某会话的未读数（Redis Hash + 总数计数器）
 func (c *ConversationCache) IncrementUnread(ctx context.Context, userID, convID string) error {
 	hashKey := UnreadHashKey(userID)