CVE-2026-43982 Algernon: Path traversal file write via savein()

Algernon is a small self-contained pure-Go web server. Prior to 1.17.6, uploadedFileSaveIn in lua/upload/upload.go uses filepath.Join with the caller-supplied directory but performs no boundary check after joining. A directory of ../../../tmp resolves cleanly to /tmp, outside the web root. This...