refactor: cleanup unused code and simplify internal packages

This commit performs a significant cleanup of the codebase by removing unused functions, methods, and entire files across various internal modules. This reduces technical debt and simplifies the project structure.

Key changes include:
- **cache**: Removed unused cache key generators and metrics snapshots.
- **dto**: Removed redundant converter functions and segment creation helpers.
- **middleware**: Deleted the unused `logger.go` middleware and simplified `ratelimit.go` and `casbin.go`.
- **model**: Removed unused ID helpers, database closing functions, and batch decryption logic.
- **pkg**: Cleaned up unused utility functions in `circuitbreaker`, `crypto`, `cursor`, `hook`, and `utils`.
- **service**: Deleted `account_cleanup_service.go` and removed unused helper functions in `log_cleanup_service.go` and `sensitive_service.go`.
- **repository**: Removed unused private loading methods in `comment_repo.go`.

internal/dto/notification_converter.go

@@ -33,49 +33,6 @@ func ConvertNotificationsToResponse(notifications []*model.Notification) []*Noti
 	return result
 }
 
-// ==================== SystemMessage 转换 ====================
-
-// SystemMessageToResponse 将Message转换为SystemMessageResponse
-func SystemMessageToResponse(msg *model.Message) *SystemMessageResponse {
-	if msg == nil {
-		return nil
-	}
-
-	// 从 segments 中提取文本内容
-	content := ExtractTextContentFromModel(msg.Segments)
-
-	resp := &SystemMessageResponse{
-		ID:         msg.ID,
-		SenderID:   msg.SenderID,
-		ReceiverID: "", // 系统消息的接收者需要从上下文获取
-		Content:    content,
-		Category:   string(msg.Category),
-		SystemType: string(msg.SystemType),
-		CreatedAt:  msg.CreatedAt,
-	}
-	if msg.ExtraData != nil {
-		resp.ExtraData = map[string]any{
-			"actor_id":    msg.ExtraData.ActorID,
-			"actor_name":  msg.ExtraData.ActorName,
-			"avatar_url":  msg.ExtraData.AvatarURL,
-			"target_id":   msg.ExtraData.TargetID,
-			"target_type": msg.ExtraData.TargetType,
-			"action_url":  msg.ExtraData.ActionURL,
-			"action_time": msg.ExtraData.ActionTime,
-		}
-	}
-	return resp
-}
-
-// SystemMessagesToResponse 将Message列表转换为SystemMessageResponse列表
-func SystemMessagesToResponse(messages []*model.Message) []*SystemMessageResponse {
-	result := make([]*SystemMessageResponse, 0, len(messages))
-	for _, msg := range messages {
-		result = append(result, SystemMessageToResponse(msg))
-	}
-	return result
-}
-
 // SystemNotificationToResponse 将SystemNotification转换为SystemMessageResponse
 func SystemNotificationToResponse(n *model.SystemNotification) *SystemMessageResponse {
 	if n == nil {
@@ -118,11 +75,3 @@ func SystemNotificationToResponse(n *model.SystemNotification) *SystemMessageRes
 	return resp
 }
 
-// SystemNotificationsToResponse 将SystemNotification列表转换为SystemMessageResponse列表
-func SystemNotificationsToResponse(notifications []*model.SystemNotification) []*SystemMessageResponse {
-	result := make([]*SystemMessageResponse, 0, len(notifications))
-	for _, n := range notifications {
-		result = append(result, SystemNotificationToResponse(n))
-	}
-	return result
-}