feat: convert file manager into a plugin

plugins/file-manager/src/frontend/sftp-transfer-utils.ts

@@ -0,0 +1,26 @@
+export function normalizeRemoteDir(remotePath: string): string {
+  const trimmed = remotePath.trim().replace(/\\/g, "/");
+  if (!trimmed) return "/";
+  const collapsed = trimmed.replace(/\/+/g, "/");
+  const absolute = collapsed.startsWith("/") ? collapsed : `/${collapsed}`;
+  if (absolute === "/") return "/";
+  return absolute.replace(/\/+$/, "");
+}
+
+export function joinRemotePath(basePath: string, childPath: string): string {
+  const base = normalizeRemoteDir(basePath);
+  const child = childPath.replace(/\\/g, "/").replace(/^\/+/, "");
+  if (!child) return base;
+  return base === "/" ? `/${child}` : `${base}/${child}`;
+}
+
+export function hasSameHostTransferConflict(
+  sourcePaths: string[],
+  destinationDir: string,
+): boolean {
+  const dest = normalizeRemoteDir(destinationDir);
+  return sourcePaths.some((sourcePath) => {
+    const source = normalizeRemoteDir(sourcePath);
+    return dest === source || dest.startsWith(`${source}/`);
+  });
+}