An installer that had only ever met Arch

`deploy/lxc-install.sh` had never been executed -- there was no Proxmox host
to run it on, and PLAN.md said so rather than letting it read as tested. It
was reviewed and `bash -n` checked, which is not the same claim. Running it
for the first time found two Arch-isms in `install.sh`, the script it wraps,
and only a Debian machine could have found either.

`python -m venv` is the one that mattered. On Arch `python` is Python 3, so
the bare name had worked on the only machine this had ever run on. Debian has
no `python` at all unless somebody installed `python-is-python3`, and the LXC
bootstrap installs `python3` -- so the install aborted at the virtualenv step,
with the service user, the bind mount and the clone already in place. It is
`python3` now, which is right on both.

`--shell /usr/bin/nologin` is the one that did not. That is where Arch keeps
nologin and not where Debian does, but nothing ever invoked it: `sudo -u`
execs the command directly and systemd's `User=` never reads a shell. The
account worked while pointing at a file that was not there. `/usr/sbin/nologin`
is correct on Debian and resolves on Arch too, whose `/usr/sbin` is a symlink
to `bin`.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -16,6 +16,26 @@ for 1.0.0 have something to be assembled from.
 
 ## Unreleased
 
+## 1.0.3
+
+Two Arch-isms in the installer, both of which only a Debian machine could find.
+`deploy/lxc-install.sh` had never been executed — it was reviewed and
+syntax-checked, which is not the same claim — and running it is what found them.
+
+- Fixed: **`deploy/install.sh` could not create its virtualenv on Debian**, and
+  so `deploy/lxc-install.sh` could not finish. It called bare `python`, which is
+  Python 3 on Arch — the machine this was written and only ever run on — and
+  does not exist on Debian at all unless `python-is-python3` is installed. The
+  LXC bootstrap installs `python3`, so the install aborted at the virtualenv
+  step with the service user, the bind mount and the clone already made. It now
+  calls `python3`, which is right on both.
+- Fixed: the service account was created with `--shell /usr/bin/nologin`, which
+  is where Arch keeps it and where Debian does not. Nothing invoked it — `sudo -u`
+  execs directly and systemd's `User=` never reads a shell — so the account
+  worked either way, but it was created pointing at a file that was not there.
+  Now `/usr/sbin/nologin`, which is correct on Debian and resolves on Arch too,
+  since Arch's `/usr/sbin` is a symlink to `bin`.
+
 ## 1.0.2
 
 - **The documentation moved to the [wiki](https://git.houmeres.sk/Houmeres/LLeMbas/wiki).**