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/handler/ws_handler.go

@@ -140,14 +140,15 @@ func (h *WSHandler) HandleWebSocket(c *gin.Context) {
 	// 3. 创建客户端
 	clientID := atomic.AddUint64(&h.clientSeq, 1)
 	client := &ws.Client{
-		ID:     clientID,
-		UserID: userID,
-		Send:   make(chan []byte, defaultUserBufferSize),
-		Quit:   make(chan struct{}),
+		ID:          clientID,
+		UserID:      userID,
+		Send:        make(chan []byte, defaultUserBufferSize),
+		Quit:        make(chan struct{}),
+		PendingAcks: make(map[string]time.Time),
 	}
 
 	// 4. 注册客户端
-	replayEvents, regErr := h.wsHub.Register(client)
+	regErr := h.wsHub.Register(client)
 	if regErr != nil {
 		zap.L().Warn("WebSocket registration rejected",
 			zap.String("user_id", userID),
@@ -165,23 +166,18 @@ func (h *WSHandler) HandleWebSocket(c *gin.Context) {
 		zap.Uint64("client_id", clientID),
 	)
 
-	// 5. 发送历史回放消息
-	go func() {
-		for _, ev := range replayEvents {
-			msg := ws.ResponseMessage{
-				EventID: ev.ID,
-				Type:    ev.Type,
-				TS:      ev.TS,
-				Payload: ev.Payload,
-			}
-			data, _ := json.Marshal(msg)
-			select {
-			case <-client.Quit:
-				return
-			case client.Send <- data:
-			}
+	// 5. 提示客户端进行 seq 同步
+	syncMsg := ws.ResponseMessage{
+		EventID: h.wsHub.NextID(),
+		Type:    "sync_required",
+		TS:      time.Now().UnixMilli(),
+	}
+	if syncData, err := json.Marshal(syncMsg); err == nil {
+		select {
+		case <-client.Quit:
+		case client.Send <- syncData:
 		}
-	}()
+	}
 
 	// 6. 启动读写goroutine
 	go h.writePump(conn, client)
@@ -322,6 +318,8 @@ func (h *WSHandler) handleMessage(client *ws.Client, msg *ws.Message) {
 		h.handleRead(ctx, client, msg.Payload)
 	case "recall":
 		h.handleRecall(ctx, client, msg.Payload)
+	case "ack":
+		h.handleAck(client, msg.Payload)
 	// 通话信令
 	case "call_invite":
 		h.handleCallInvite(ctx, client, msg.Payload)
@@ -511,6 +509,17 @@ func (h *WSHandler) handleRecall(ctx context.Context, client *ws.Client, payload
 
 const defaultUserBufferSize = 128
 
+// handleAck 处理客户端ACK确认
+func (h *WSHandler) handleAck(client *ws.Client, payload json.RawMessage) {
+	var req struct {
+		MessageID string `json:"message_id"`
+	}
+	if err := json.Unmarshal(payload, &req); err != nil || req.MessageID == "" {
+		return
+	}
+	h.wsHub.AckMessage(client.UserID, req.MessageID)
+}
+
 // isVerified 检查用户是否已通过身份认证
 func (h *WSHandler) isVerified(ctx context.Context, client *ws.Client) bool {
 	user, err := h.userRepo.GetByID(client.UserID)