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/dto/trade_converter.go

@@ -45,8 +45,8 @@ func ConvertTradeItemToResponse(item *model.TradeItem, isFavorited bool) *TradeI
 		FavoritesCount: item.FavoritesCount,
 		IsFavorited:    isFavorited,
 		Images:         ConvertTradeImagesToResponse(item.Images),
-		CreatedAt:      item.CreatedAt.Format("2006-01-02T15:04:05Z07:00"),
-		UpdatedAt:      item.UpdatedAt.Format("2006-01-02T15:04:05Z07:00"),
+		CreatedAt:      FormatTime(item.CreatedAt),
+		UpdatedAt:      FormatTime(item.UpdatedAt),
 	}
 	if len(item.Segments) > 0 {
 		resp.Segments = item.Segments
@@ -66,32 +66,6 @@ func ConvertTradeItemsToResponse(items []*model.TradeItem, favoriteMap map[strin
 	return result
 }
 
-func ConvertTradeItemToDetailResponse(item *model.TradeItem, isFavorited bool) *TradeItemDetailResponse {
-	if item == nil {
-		return nil
-	}
-	resp := &TradeItemDetailResponse{
-		ID:             item.ID,
-		UserID:         item.UserID,
-		TradeType:      string(item.TradeType),
-		Category:       string(item.Category),
-		Title:          item.Title,
-		Content:        item.Content,
-		Price:          item.Price,
-		Condition:      item.Condition,
-		Status:         string(item.Status),
-		ViewsCount:     item.ViewsCount,
-		FavoritesCount: item.FavoritesCount,
-		IsFavorited:    isFavorited,
-		Images:         ConvertTradeImagesToResponse(item.Images),
-		CreatedAt:      item.CreatedAt.Format("2006-01-02T15:04:05Z07:00"),
-		UpdatedAt:      item.UpdatedAt.Format("2006-01-02T15:04:05Z07:00"),
-	}
-	if len(item.Segments) > 0 {
-		resp.Segments = item.Segments
-	}
-	if item.User != nil {
-		resp.Author = ConvertUserToResponse(item.User)
-	}
-	return resp
+func ConvertTradeItemToDetailResponse(item *model.TradeItem, isFavorited bool) *TradeItemResponse {
+	return ConvertTradeItemToResponse(item, isFavorited)
 }