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.

deploy.sh

@@ -1,7 +1,9 @@
 #!/usr/bin/env bash
 #
 # Builds the image with podman, pushes it to the private registry, then deploys
-# the Site with the playbook that lives in ansible/.
+# the Site with the playbook that lives in ansible/. The playbook runs rootless
+# Podman Quadlet units on emily, behind the shared Caddy unit from
+# ansible-playbooks/caddy.
 #
 #   ./deploy.sh 2026-09-22                  deploy the default Site
 #   SITE=greatbear ./deploy.sh 2026-09-22   deploy another Site
@@ -24,6 +26,11 @@ if ! command -v podman >/dev/null 2>&1; then
   exit 1
 fi
 
+if [[ -z "${SKIP_DEPLOY:-}" ]] && ! command -v ansible-playbook >/dev/null 2>&1; then
+  echo "ansible-playbook is required to deploy; SKIP_DEPLOY=1 builds and pushes only" >&2
+  exit 1
+fi
+
 if [[ -z "${SKIP_CHECKS:-}" ]]; then
   echo "==> lint, format, types and tests"
   npm run lint