Downloads fail on Linux containers when filenames contain square
brackets or multiple consecutive spaces. On Linux, .NET's
Path.GetInvalidFileNameChars() only returns NUL and '/', so characters
like [ ] { } that cause issues with shell globbing, URI handling, and
various download clients pass through the existing filter unchanged.
Add FilenameSanitizer that:
- Strips square brackets, curly braces, and control characters
- Collapses multiple consecutive spaces into one
- Trims leading and trailing whitespace
- Preserves parentheses and all other characters
Apply sanitization at filesystem boundaries: DownloadHelper (where the
Real-Debrid filename is turned into a local path), UnpackClient,
Torrent delete / RunOnTorrentComplete, and the qBittorrent / SABnzbd
status paths that *arr reads back. Aria2c and DownloadStation also
sanitize their remote output paths so they match the sanitized local
filePath. Symlink's rclone-mount lookup still uses the original name
since that has to match the real file in the mount.
Add a SanitizeFilenames toggle in DbSettings (default on) so users
can disable the behaviour if they need the exact Real-Debrid name.
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