docs(download_file): annotate filename sanitization purpose

Agent-Logs-Url: https://github.com/fabiocaccamo/python-fsutil/sessions/79e7623b-5e54-484b-838b-9b58f5877733

Co-authored-by: fabiocaccamo <1035294+fabiocaccamo@users.noreply.github.com>

Author: Copilot

src/fsutil/operations.py

@@ -213,6 +213,7 @@ def download_file(
             filename_pattern = r'filename="(.*)"'
             filename_match = re.search(filename_pattern, content_disposition)
             if filename_match:
+                # sanitize Content-Disposition filename to prevent path traversal
                 filename = os.path.basename(filename_match.group(1))
             # or detect filename from url
             if not filename: