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/pkg/response/response.go

@@ -111,21 +111,6 @@ func Paginated(c *gin.Context, list any, total int64, page, pageSize int) {
 	})
 }
 
-// HandleServiceError 统一处理 Service 错误
-// 如果 err 是 *apperrors.AppError，返回对应的业务错误码和消息
-// 如果 err 是其他错误，返回 false（调用方应处理通用错误）
-// 返回 true 表示错误已处理，false 表示需要调用方继续处理
-func HandleServiceError(c *gin.Context, err error) bool {
-	if err == nil {
-		return false
-	}
-	if se, ok := apperrors.As(err); ok {
-		statusCode := statusCodeFromAppErrorCode(se.Code)
-		ErrorWithStringCode(c, statusCode, se.Code, se.Message)
-		return true
-	}
-	return false
-}
 
 // HandleError 统一处理错误（带默认消息）
 // 如果 err 是 *apperrors.AppError，返回对应的业务错误码和消息