Desktop sessions (e.g. KDE launched from a display manager) often lack
~/.local/bin on PATH, so the relative Exec=signaltty-gui failed with
"could not find the program". The installer now writes the installed
binary's quoted absolute path into the entry and refuses prefixes whose
characters would need Desktop Entry escaping.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>