File writes and deletions via unchecked backup path

Path traversal in Streambert before 2.6.0 allows local users with renderer control to write or delete files via a crafted backup path. The perform-scheduled-backup IPC handler passes renderer-supplied settings.path directly to directory creation, JSON writing, directory listing, and pruning operations without confining it to an authorized backup location. Exploitation requires control of the Electron renderer and can create directories, write timestamped JSON containing controlled data, or delete matching backup-named JSON files under the chosen path.