refactor: improve system stability, performance, and code structure

This commit introduces several architectural improvements and optimizations across the codebase:

- **Performance & Reliability**:
  - Implemented Redis pipelining in `ConversationCache.CacheMessage` to reduce network round-trips.
  - Added a circuit breaker to the JPush client to prevent cascading failures.
  - Introduced batch deletion and batch member addition capabilities in repositories.
  - Added message idempotency support using `client_msg_id` and a Redis-based cache.
  - Optimized WebSocket handling with connection limits (total and per-user) and improved error logging.

- **Code Refactoring**:
  - Refactored `Router` to use a `RouterDeps` struct, simplifying the constructor and improving maintainability.
  - Unified model ID generation logic using new `id_helper.go` (supporting UUID and Snowflake).
  - Standardized JSON serialization/deserialization in models using `json_helper.go`.
  - Refactored DTO conversion logic, specifically for `UserResponse` (using functional options) and `Report` responses.
  - Removed redundant/deprecated DTOs like `PostDetailResponse` and `TradeItemDetailResponse`.

- **Cache Improvements**:
  - Enhanced `LayeredCache` with `SetRaw` to avoid double-encoding when promoting values from Redis to local cache.
  - Added `DeleteBatch` support to the cache interface.

- **Other Changes**:
  - Cleaned up `config.go` by removing redundant default values and explicit environment variable overrides.
  - Improved WebSocket registration flow to handle connection limits gracefully.

internal/handler/ws_handler.go

@@ -147,7 +147,17 @@ func (h *WSHandler) HandleWebSocket(c *gin.Context) {
 	}
 
 	// 4. 注册客户端
-	replayEvents := h.wsHub.Register(client)
+	replayEvents, regErr := h.wsHub.Register(client)
+	if regErr != nil {
+		zap.L().Warn("WebSocket registration rejected",
+			zap.String("user_id", userID),
+			zap.Error(regErr),
+		)
+		conn.WriteMessage(websocket.CloseMessage,
+			[]byte(`{"type":"error","payload":{"code":"connection_limit","message":"too many connections"}}`))
+		conn.Close()
+		return
+	}
 	defer h.wsHub.Unregister(client)
 
 	zap.L().Info("WebSocket client connected",
@@ -264,6 +274,11 @@ func (h *WSHandler) writePump(conn *websocket.Conn, client *ws.Client) {
 
 			w, err := conn.NextWriter(websocket.TextMessage)
 			if err != nil {
+				zap.L().Warn("WebSocket write error (NextWriter)",
+					zap.String("user_id", client.UserID),
+					zap.Uint64("client_id", client.ID),
+					zap.Error(err),
+				)
 				return
 			}
 			w.Write(message)
@@ -276,6 +291,11 @@ func (h *WSHandler) writePump(conn *websocket.Conn, client *ws.Client) {
 			}
 
 			if err := w.Close(); err != nil {
+				zap.L().Warn("WebSocket write error (Close)",
+					zap.String("user_id", client.UserID),
+					zap.Uint64("client_id", client.ID),
+					zap.Error(err),
+				)
 				return
 			}
 		case <-ticker.C:
@@ -349,6 +369,7 @@ func (h *WSHandler) handleChat(ctx context.Context, client *ws.Client, payload j
 		DetailType     string                `json:"detail_type"`
 		Segments       model.MessageSegments `json:"segments"`
 		ReplyToID      *string               `json:"reply_to_id,omitempty"`
+		ClientMsgID    string                `json:"client_msg_id,omitempty"`
 	}
 
 	if err := json.Unmarshal(payload, &req); err != nil {
@@ -367,7 +388,7 @@ func (h *WSHandler) handleChat(ctx context.Context, client *ws.Client, payload j
 	}
 
 	// 发送消息
-	message, err := h.chatService.SendMessage(ctx, client.UserID, req.ConversationID, req.Segments, req.ReplyToID)
+	message, err := h.chatService.SendMessage(ctx, client.UserID, req.ConversationID, req.Segments, req.ReplyToID, req.ClientMsgID)
 	if err != nil {
 		h.wsHub.SendError(client, "send_failed", err.Error())
 		return