Collapse the 5-distro matrix in the make and pkgmgr install-test workflows
into a single job that runs every distro in parallel inside extracted
scripts, cutting 5 runners down to 1 per workflow. Each distro installs
against its own copy of the checkout so the concurrent in-container builds
never race on the shared tree. The distro list is read from the
INFINITO_DISTROS SPOT in default.env instead of being hardcoded.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>