GHSA-2956-977x-2w3r: Flyto2 Core: Arbitrary file write via image.download (and other file-writing modules)

Flyto2 Core has a file-writing vulnerability in `image.download` and 12 other file-writing modules (like `image.convert`, `document.pdf_fill_form`, etc.) that allows attackers to write files anywhere on the system. The problem is that these modules check whether the target file is within a base directory, but the attacker controls both the target file path and the base directory parameter, making the check useless. For example, if an attacker sets `output_dir='/'`, any target path passes the validation, and the attacker's data (from a URL or format operation) gets written to any location the process can access.