feat(core): optimize performance and reliability through batching and redis-backed unread counts

This commit introduces several significant architectural improvements to enhance system performance, scalability, and reliability:

- **Performance Optimization (N+1 Problem Resolution)**: Implemented batching mechanisms across `MessageHandler`, `ChatService`, `GroupService`, `MessageService`, and `UserService`. This replaces multiple individual database/cache queries with single batch operations for fetching unread counts, last messages, participants, and user information.
- **Enhanced Unread Count Management**: Migrated unread count tracking to a Redis Hash-based approach (`unread#️⃣{userID}`). This allows for atomic increments/decrements and efficient retrieval of both individual conversation unread counts and total unread counts for a user.
- **Improved Message Sequencing**: Integrated Redis-based sequence (`seq`) pre-allocation for messages to ensure strict ordering and reduce database contention during high-concurrency message creation.
- **Push Service Reliability**: Refactored the push notification system to include persistent `PushRecord` tracking. Added a recovery mechanism (`recoverPendingPushes`) to reload pending notifications from the database upon service startup, ensuring better delivery guarantees.
- **WebSocket Reliability**: Updated the WebSocket hub to move away from in-memory history replay in favor of a client-driven synchronization model (`sync_required` event and `ack` handling), reducing memory overhead and improving connection stability.
- **Cache Layer Enhancements**: Added `HIncrBy` and `IncrBySeq` to the `Cache` interface and its implementations (`RedisCache`, `LayeredCache`) to support the new unread and sequence management logic.

internal/service/group_service.go

@@ -61,6 +61,7 @@ type GroupService interface {
 	TransferOwner(userID string, groupID string, newOwnerID string) error
 	GetUserGroups(userID string, page, pageSize int) ([]model.Group, int64, error)
 	GetMemberCount(groupID string) (int, error)
+	GetMemberCountBatch(ctx context.Context, groupIDs []string) (map[string]int64, error)
 
 	// 成员管理
 	InviteMembers(userID string, groupID string, memberIDs []string) error
@@ -106,25 +107,36 @@ type GroupMembersResult struct {
 
 // groupService 群组服务实现
 type groupService struct {
-	groupRepo   repository.GroupRepository
-	userRepo    repository.UserRepository
-	messageRepo repository.MessageRepository
-	requestRepo repository.GroupJoinRequestRepository
-	notifyRepo  repository.SystemNotificationRepository
-	wsHub       *ws.Hub
-	cache       cache.Cache
+	groupRepo         repository.GroupRepository
+	userRepo          repository.UserRepository
+	messageRepo       repository.MessageRepository
+	requestRepo       repository.GroupJoinRequestRepository
+	notifyRepo        repository.SystemNotificationRepository
+	wsHub             *ws.Hub
+	cache             cache.Cache
+	conversationCache *cache.ConversationCache
 }
 
 // NewGroupService 创建群组服务
 func NewGroupService(groupRepo repository.GroupRepository, userRepo repository.UserRepository, messageRepo repository.MessageRepository, requestRepo repository.GroupJoinRequestRepository, notifyRepo repository.SystemNotificationRepository, wsHub *ws.Hub, cacheBackend cache.Cache) GroupService {
+	convRepoAdapter := cache.NewConversationRepositoryAdapter(messageRepo)
+	msgRepoAdapter := cache.NewMessageRepositoryAdapter(messageRepo)
+	conversationCache := cache.NewConversationCache(
+		cacheBackend,
+		convRepoAdapter,
+		msgRepoAdapter,
+		cache.DefaultConversationCacheSettings(),
+	)
+
 	return &groupService{
-		groupRepo:   groupRepo,
-		userRepo:    userRepo,
-		messageRepo: messageRepo,
-		requestRepo: requestRepo,
-		notifyRepo:  notifyRepo,
-		wsHub:       wsHub,
-		cache:       cacheBackend,
+		groupRepo:         groupRepo,
+		userRepo:          userRepo,
+		messageRepo:       messageRepo,
+		requestRepo:       requestRepo,
+		notifyRepo:        notifyRepo,
+		wsHub:             wsHub,
+		cache:             cacheBackend,
+		conversationCache: conversationCache,
 	}
 }
 
@@ -299,6 +311,11 @@ func (s *groupService) GetMemberCount(groupID string) (int, error) {
 	return int(count), nil
 }
 
+// GetMemberCountBatch 批量获取多个群的成员数量
+func (s *groupService) GetMemberCountBatch(ctx context.Context, groupIDs []string) (map[string]int64, error) {
+	return s.groupRepo.GetMemberCountBatch(ctx, groupIDs)
+}
+
 // UpdateGroup 更新群组信息
 func (s *groupService) UpdateGroup(userID string, groupID string, updates map[string]any) error {
 	// 检查群组是否存在
@@ -453,6 +470,18 @@ func (s *groupService) broadcastMemberJoinNotice(groupID string, targetUserID st
 				Status:   model.MessageStatusNormal,
 				Category: model.CategoryNotification,
 			}
+			// 从 Redis 获取下一个 seq
+			if s.conversationCache != nil {
+				seq, seqErr := s.conversationCache.GetNextSeq(context.Background(), conv.ID)
+				if seqErr != nil {
+					zap.L().Warn("redis get next seq failed, falling back to DB",
+						zap.String("convID", conv.ID),
+						zap.Error(seqErr),
+					)
+				} else {
+					msg.Seq = seq
+				}
+			}
 			if err := s.messageRepo.CreateMessageWithSeq(msg); err != nil {
 				zap.L().Warn("保存入群提示消息失败",
 					zap.String("component", "broadcastMemberJoinNotice"),
@@ -1366,7 +1395,19 @@ func (s *groupService) MuteMember(userID string, groupID string, targetUserID st
 				Category: model.CategoryNotification,
 			}
 
-			// 保存消息并获取 seq
+			// 从 Redis 获取下一个 seq
+			if s.conversationCache != nil {
+				seq, seqErr := s.conversationCache.GetNextSeq(context.Background(), conv.ID)
+				if seqErr != nil {
+					zap.L().Warn("redis get next seq failed, falling back to DB",
+						zap.String("convID", conv.ID),
+						zap.Error(seqErr),
+					)
+				} else {
+					msg.Seq = seq
+				}
+			}
+
 			if err := s.messageRepo.CreateMessageWithSeq(msg); err != nil {
 				zap.L().Warn("保存禁言消息失败",
 					zap.String("component", "MuteMember"),