fix: use json.dumps(paths) for getinfo multi-path, delete probe script

DSM accepts multiple paths as a JSON array string, not comma-separated.
Comma-separated is treated as a single literal path; repeated path[]
params return error 400. Confirmed via test_getinfo_multipath.py.

- get_info: path param changed from ",".join(paths) to json.dumps(paths)
- tests: update multi-path assertion to expect JSON array format

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_tools_filestation.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import json
 from unittest.mock import AsyncMock, MagicMock
 
 import pytest
@@ -369,9 +370,9 @@ async def test_get_info_multiple_paths(config: AppConfig) -> None:
     assert "/data/b.txt" in result
     assert "2 item(s)" in result
 
-    # Verify the API received both paths as a comma-joined string
+    # Verify the API received paths as a JSON array (confirmed working format)
     call_params = client.request.call_args[1]["params"]
-    assert call_params["path"] == "/dev/a.txt,/data/b.txt"
+    assert call_params["path"] == json.dumps(["/dev/a.txt", "/data/b.txt"])
 
 
 @pytest.mark.asyncio