fix: 修复完整镜像源地址及 CRLF 任务导入 (#3093)

* fix: address six verified legacy issue regressions

* fix: limit issue patch to mirror URLs and CRLF imports

* fix: preserve APT formats and third-party repositories

test/back/linux-mirror-result.test.cjs

@@ -129,7 +129,7 @@ Acquire::http::Timeout "1";
           'fs/promises': {
             readFile: async (file) =>
               file === '/etc/os-release'
-                ? distribution
+                ? `${distribution}\nVERSION_CODENAME=bookworm\n`
                 : existingMirror
                 ? 'URIs: http://old.example/debian\n'
                 : '',