fix(ssh): treat symlinked directories as folders

[Jinwoo-H]

Summary

Follow-up to #1661 and #1672.

PR #1672 removed the SSH relay path allowlist so symlink targets outside the workspace can be opened, but directory symlinks were still misclassified by directory listings:

• fs.readDir used Dirent.isDirectory(), which returns false for symlink entries.
• The file explorer therefore treated a symlink-to-directory like a file.
• Clicking it called readFile, which failed with EISDIR: illegal operation on a directory, read.

This PR makes directory listings report symlink-to-directory entries as directories while preserving isSymlink: true.

What changed

• Relay fs.readDir follows symlink entries with stat() only to determine whether the target is a directory.
• Relay fs.stat returns the target file/directory type for symlinks, falling back to symlink for broken links.
• Local fs:readDir gets the same symlink-to-directory behavior, but still resolves through the existing authorized-path boundary.
• Added regression coverage for directory symlinks in both relay and local filesystem tests.

Verification

• pnpm test src/relay/fs-handler.test.ts src/main/ipc/filesystem.test.ts
• pnpm tc:node
• Manual SSH repro on openclaw 2 using /home/jinwoo/Documents/repo-test/Model -> /tmp/orca-repo-test-symlink-target

Note: local commands emitted the existing Node engine warning because this machine is on Node v25.9.0 while the repo wants Node 24, but both commands passed.

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