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>

src/mcp_synology_filestation/tools/filestation.py

@@ -238,7 +238,7 @@ def register_filestation(
                 "SYNO.FileStation.List",
                 "getinfo",
                 params={
-                    "path": ",".join(paths),
+                    "path": json.dumps(paths),
                     "additional": json.dumps(
                         ["real_path", "size", "time", "perm", "owner", "type"]
                     ),