refactor(ota): 优化文件路径计算逻辑

- 将 root_path() 函数调用替换为 ROOT_PATH 常量
- 提高代码可读性和性能
- 统一路径常量使用方式

application/api/controller/Ota.php

@@ -131,7 +131,7 @@ class Ota extends Api
      */
     private function calculateFileInfo($relativePath)
     {
-        $fullPath = root_path() . 'public' . DIRECTORY_SEPARATOR . 'uploads' . DIRECTORY_SEPARATOR . ltrim($relativePath, '/');
+        $fullPath = ROOT_PATH . 'public' . DIRECTORY_SEPARATOR . 'uploads' . DIRECTORY_SEPARATOR . ltrim($relativePath, '/');
         if (!file_exists($fullPath)) {
             return null;
         }