Introduces a full-stack Test Sandbox feature to run distro matrix tests in Docker from the UI: new backend API/service, sandbox_runs model + migration, run/log endpoints, and a new frontend page with mode selection, run history, live polling, cancel, and per-distro logs.
Also adds ARM64 scripts CI coverage (ubuntu-24.04-arm) and strengthens install/test automation for minimal images and overlay rebuilds: early curl/bootstrap index refresh, stricter venv validation, release-venv glibc fallback, Node reprovisioning on source fallback, rsync --delete overlay behavior, npm bootstrap in VM install, Windows tar pinning in PowerShell harness, plus updated test docs and distro coverage notes.
