CLSA-2026-1777457441 python: Fix of 2 CVEs

CVE-2026-4519: reject webbrowser.open URLs with a leading dash to prevent CLI option injection into the spawned browser process - CVE-2026-4786: validate URLs after %action substitution and swap the substitution order in UnixBrowser.open to close a bypass of the CVE-2026-4519 dash-prefix check...