rexenv 0.8.8

The first release with Linux — Ubuntu 22.04+ .deb and AppImage for x86_64 and aarch64 (self-update, PHP 7.4, the dummy-link DNS route, both trust stores) — and the first built entirely on GitHub Actions: one tag, every OS, one draft on the tap. Also: the deb depends on pkexec | policykit-1 and declares PostgreSQL's libraries; MySQL and PostgreSQL load on Ubuntu 24.04+/26.04 through rexenv's lib-compat shims; 'CA trusted' on Linux means both stores; a test helper's /bin/kill no longer takes the whole process group with it on Linux.