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/call_dto.go

@@ -143,49 +143,3 @@ type CallConfigResponse struct {
 	ICEServers []ICEServerConfig `json:"ice_servers"`
 }
 
-// ==================== Converter Functions ====================
-
-// ConvertCallSessionToResponse 转换通话会话为响应格式
-func ConvertCallSessionToResponse(call *model.CallSession, caller *model.User, participants []*model.User) *CallSessionResponse {
-	resp := &CallSessionResponse{
-		ID:             call.ID,
-		ConversationID: call.ConversationID,
-		CallerID:       call.CallerID,
-		CallType:       call.CallType,
-		Status:         call.Status,
-		StartedAt:      call.StartedAt,
-		EndedAt:        call.EndedAt,
-		Duration:       call.Duration,
-		CreatedAt:      call.CreatedAt,
-	}
-
-	if call.GroupID != nil {
-		resp.GroupID = *call.GroupID
-	}
-
-	if caller != nil {
-		resp.Caller = ConvertUserToResponse(caller)
-	}
-
-	// 转换参与者
-	resp.Participants = make([]CallParticipantResponse, 0, len(call.Participants))
-	userMap := make(map[string]*model.User)
-	for _, u := range participants {
-		userMap[u.ID] = u
-	}
-
-	for _, p := range call.Participants {
-		pr := CallParticipantResponse{
-			UserID:   p.UserID,
-			Status:   p.Status,
-			JoinedAt: p.JoinedAt,
-			LeftAt:   p.LeftAt,
-		}
-		if u, ok := userMap[p.UserID]; ok {
-			pr.User = ConvertUserToResponse(u)
-		}
-		resp.Participants = append(resp.Participants, pr)
-	}
-
-	return resp
-}