Run the Sites as rootless Podman Quadlets, and build with podman

The fleet on emily is rootless Podman with Quadlet units under
~/.config/containers/systemd and state in ~/podman-data, all behind one shared
Caddy unit. This brings the menus in line instead of leaving them the last
Docker deployment. The build moves with them: podman reads a Containerfile as
readily as a Dockerfile, so the name now says which toolchain is real.

The app is one .container and one .network file. Two details carry it.
UserNS=keep-id maps the image's own node account onto the user that owns the
units, so data/ and site.env stay owned by tanshu: plain tar backups, no
subuids. provision-site-env.sh writes site.env with the same mapping rather
than --user, which under rootless Podman would have produced a subuid-owned
file the app could not read. And the Site registers its own network with Caddy
by writing a drop-in beside caddy.container, so Caddy never lists its upstreams
and never changes when a Site is added. The unit keeps the Docker-era container
name for the scripts and muscle memory that look it up, while the Caddyfile
proxies to a dotless NetworkAlias, because a container name with dots in it is
a liability in DNS.

The unit keeps podman's Pull=missing, so a restart or a reboot never depends on
the registry being reachable, while the play pulls explicitly at deploy time.
That is also where a missing `podman login` for the private registry now fails,
with the instruction, rather than as a unit that will not start.

copy-site-data.sh moves a Site's data across, and is not a plain rsync:
/var/lib/menu.* on monoco belongs to uid 1000 while the ssh user there is 1001,
so the read needs sudo; monoco cannot ssh to emily, so the workstation relays
the tar; and the extraction runs as tanshu on emily, which is what makes the
files land owned by the user keep-id maps the app onto. It proves the copy by
comparing a SHA-256 of the whole tree against the source and checking every
file's owner.

Not yet done: the copies themselves and the DNS move, which need a human.

ansible/roles/menu-app/templates/menu-app.container.j2

@@ -0,0 +1,60 @@
+# {{ container_name }} — rootless Podman Quadlet unit.
+# Managed by Ansible (menu-admin/roles/menu-app). Do not edit by hand.
+#
+# Joins {{ network_name }}.network, written by roles/register — the same include
+# that attaches Caddy to it. Caddy reaches the app by container name, so nothing
+# is published on the host and the app is not reachable from outside the Podman
+# network at all.
+
+[Unit]
+Description=Menu app for {{ host }}
+After=network-online.target
+Wants=network-online.target
+
+[Container]
+ContainerName={{ container_name }}
+Image={{ image_name }}:{{ image_tag }}
+
+# keep-id maps the image's own account — `node`, uid/gid {{ app_uid }} — onto
+# {{ podman_user }}, which is what keeps every file the app writes owned by
+# {{ podman_user }} on the host: plain tar/rsync backups, no subuids, no
+# `podman unshare`. The same mapping is why scripts/provision-site-env.sh writes
+# site.env with --userns=keep-id.
+UserNS=keep-id:uid={{ app_uid }},gid={{ app_gid }}
+
+# The alias is deliberately dotless. ContainerName keeps the Docker-era name so
+# operators and scripts find it, but a name with dots in it is a liability in
+# DNS, so {{ network_name }} is what the Caddyfile proxies to. Both resolve from
+# inside the network.
+NetworkAlias={{ network_name }}
+
+Environment=MENU_ROOT=/data
+Environment=MENU_SITE_CONFIG=/app/config/{{ site }}.site.json
+Environment=SECURE_COOKIES=true
+Environment=LOG_LEVEL=info
+Environment=PORT={{ container_port }}
+
+# Everything the app writes: data/ (originals, drafts, published, site.json,
+# sections.json) and site.env. The Site's own config is baked into the image and
+# read from /app.
+Volume={{ app_root }}:/data
+
+Network={{ network_name }}.network
+
+# podman builds an OCI image by default and drops the Containerfile's
+# HEALTHCHECK instruction, so the same check is declared here and the play gates
+# on it with `podman healthcheck run`. node is in the image.
+HealthCmd={{ health_cmd }}
+HealthInterval=30s
+HealthTimeout=5s
+HealthRetries=3
+HealthStartPeriod=30s
+
+[Service]
+Restart=always
+# The app validates its data directory before it serves and refuses to boot on a
+# fatal integrity problem, so a first start over copied data can take a moment.
+TimeoutStartSec=120
+
+[Install]
+WantedBy=default.target