Linux: fix black window and WebKitWebProcess crash on newer distros (Fedora 40+, Ubuntu 24.04 inside distrobox, and similar). The accelerated compositor was aborting against Mesa 26 through the EGL / DMABUF stack, and the WebKit sandbox was failing silently in nested containers. Both are now bypassed at startup on Linux.
macOS and Windows are unchanged from 1.4.0. New AppImage and deb are below. Existing 1.4.0 Linux installs will auto-update; the Mac and Windows buttons on astermail.org continue to point at the 1.4.0 installers carried forward on this release.
Closes #15.