Add workaround for:
   https://github.com/Sigil-Ebook/Sigil/issues/874

--- src/Resource_Files/bash/sigil-sh_install.orig	2026-07-22 07:53:34.831031000 +1200
+++ src/Resource_Files/bash/sigil-sh_install	2026-07-22 07:54:41.043039000 +1200
@@ -24,6 +24,9 @@
 #  export SIGIL_EXTRA_ROOT
 #fi
 
+# Workaround for crash-on-close
+export QT_QUICK_BACKEND=software
+
 export LD_LIBRARY_PATH
 
 exec ${CMAKE_INSTALL_FULL_LIBDIR}/sigil/sigil "$@"