feat: add dir_size and get_md5 tools

dir_size: SYNO.FileStation.DirSize v2 — async scan of one or more
directories, returns folder/file count and total size as a table.
get_md5: SYNO.FileStation.MD5 v2 — async MD5 checksum of a file.
Both follow the existing _poll_task pattern. 9 new unit tests.

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

src/mcp_synology_filestation/tools/filestation.py

@@ -781,6 +781,101 @@ def register_filestation(
         dest = status.get("dest_folder_path", dest_folder_path)
         return f"Extracted to: {dest}"
 
+    @mcp.tool()
+    async def dir_size(path: str):
+        """Get total size, file count and folder count for one or more directories.
+        path: comma-separated share-relative paths."""
+        from mcp_synology_filestation.client import SynologyError
+
+        paths = [p.strip() for p in path.split(",") if p.strip()]
+        if not paths:
+            return "Error: no path provided."
+
+        try:
+            start_data = await client.request(
+                "SYNO.FileStation.DirSize",
+                "start",
+                version=2,
+                params={"path": json.dumps(paths)},
+            )
+        except SynologyError as e:
+            return f"Error: {e}"
+
+        taskid: str = start_data.get("taskid", "")
+        if not taskid:
+            return "Error: DSM did not return a task ID."
+
+        ok, result = await _poll_task("SYNO.FileStation.DirSize", 2, taskid)
+        if not ok:
+            return result  # type: ignore[return-value]
+
+        status: dict[str, Any] = result  # type: ignore[assignment]
+        num_dir = status.get("num_dir", 0)
+        num_file = status.get("num_file", 0)
+        total_size = status.get("total_size", 0)
+
+        path_label = ", ".join(paths)
+        w_path = max(len("Path"), len(path_label))
+        num_dir_str = str(num_dir)
+        num_file_str = str(num_file)
+        size_str = _fmt_size(total_size)
+
+        sep = (
+            f"+{'-' * (w_path + 2)}"
+            f"+{'-' * (max(len('Folders'), len(num_dir_str)) + 2)}"
+            f"+{'-' * (max(len('Files'), len(num_file_str)) + 2)}"
+            f"+{'-' * (max(len('Total Size'), len(size_str)) + 2)}+"
+        )
+        w_dir = max(len("Folders"), len(num_dir_str))
+        w_file = max(len("Files"), len(num_file_str))
+        w_size = max(len("Total Size"), len(size_str))
+
+        sep = (
+            f"+{'-' * (w_path + 2)}+{'-' * (w_dir + 2)}+{'-' * (w_file + 2)}+{'-' * (w_size + 2)}+"
+        )
+        header = (
+            f"| {'Path':<{w_path}} "
+            f"| {'Folders':<{w_dir}} "
+            f"| {'Files':<{w_file}} "
+            f"| {'Total Size':<{w_size}} |"
+        )
+        row = (
+            f"| {path_label:<{w_path}} "
+            f"| {num_dir_str:<{w_dir}} "
+            f"| {num_file_str:<{w_file}} "
+            f"| {size_str:<{w_size}} |"
+        )
+        return "\n".join([sep, header, sep, row, sep])
+
+    @mcp.tool()
+    async def get_md5(path: str):
+        """Compute the MD5 checksum of a file on the NAS. path: share-relative file path."""
+        from mcp_synology_filestation.client import SynologyError
+
+        try:
+            start_data = await client.request(
+                "SYNO.FileStation.MD5",
+                "start",
+                version=2,
+                params={"file_path": json.dumps(path)},
+            )
+        except SynologyError as e:
+            return f"Error: {e}"
+
+        taskid: str = start_data.get("taskid", "")
+        if not taskid:
+            return "Error: DSM did not return a task ID."
+
+        ok, result = await _poll_task("SYNO.FileStation.MD5", 2, taskid)
+        if not ok:
+            return result  # type: ignore[return-value]
+
+        status: dict[str, Any] = result  # type: ignore[assignment]
+        md5 = status.get("md5", "")
+        if not md5:
+            return "Error: DSM returned no MD5 hash."
+        return f"MD5 of {path}: {md5}"
+
     @mcp.tool()
     async def upload(
         path: str,