A fresh Debian template has not generated the Proxmox host locale that pct exec
forwards (e.g. fr_FR.UTF-8), so apt, perl and apt-listchanges warn on every run.
Export LC_ALL=C.UTF-8 / LANG=C.UTF-8 globally and forward them through pct exec
(base tooling, the piped installer, and the host-side upgrade).
- detect_latest_debian_template now selects the newest debian-12 template only.
Auto-detecting the newest Debian overall picked debian-13, which would pair the
deb12-only DocumentDB extension with a mismatched libicu. Trixie now requires
setting TEMPLATE + DOCUMENTDB_DISTRO explicitly.
- Add preflight_script_url: verify SCRIPT_URL is reachable on the host before
creating the LXC, so a branch/path that 404s fails immediately with guidance
instead of dying mid-install after the container is built.
