GHSA-322x-v876-g883: @asymmetric-effort/nogginlessdom's Path Traversal in matchFileSnapshot allows arbitrary file write

The matchFileSnapshot function in src/assertions/snapshots.ts accepted a filePath parameter with zero validation. When snapshot update mode was active (UPDATE_SNAPSHOTS=1 or setUpdateMode('all')), an attacker who controls test input could write arbitrary content to any filesystem path the process has write access to, including creating intermediate directories.