Arbitrary file writes via unsanitized topic paths

Path traversal in arxiv-daily through May 6, 2025 allows local users to write files outside docs/ via crafted topic.yml keys. daily_arxiv.py uses unsanitized topic and subtopic values from topic.yml when constructing output paths, so ../ segments escape the intended docs/ tree. An attacker who can modify the configuration and run generation can overwrite files writable by the process or consume disk space, causing configuration corruption or a service interruption.