Run Tandoor as a rootless Podman Quadlet

Replaces the docker_container role with a Quadlet systemd user unit, and moves
state from /var/lib/tandoor to ~/podman-data/tandoor. Tandoor's entrypoint
starts as root and drops privileges, but root is what ends up owning the data,
so keep-id maps container root onto the connecting user and everything stays
owned by tanshu rather than a subuid.

The play does not run the rootless-Podman prerequisites: they are the shared
task file at caddy/roles/podman, and a host that has run caddy/playbook.yml has
them. Both integrations go through the shared includes rather than local copies
-- caddy/roles/register for the network and the Caddy drop-in, postgres/roles/
attach for the database -- so this app writes the same drop-in bytes as every
other service and a new service never means editing Caddy or Postgres.

Three ordering details are load-bearing:

- The register include runs in pre_tasks, before the unit is started. Quadlet
  fails unit *generation*, not merely startup, when a referenced .network file
  does not exist yet, so starting first reports "unit not found".
- roles/postgres flushes handlers immediately after attaching. The restart that
  joins Postgres to this network is a handler, so by default it runs at the end
  of the play -- after the app has already started and failed to resolve `db`.
- The role waits for a real HTTP response from inside the container instead of
  trusting systemctl is-active. The entrypoint runs Django migrations before
  gunicorn answers, and until it does the image's own nginx returns 502, which
  Caddy relays verbatim -- complete with `server: nginx`, which reads as a stray
  reverse proxy that is not actually there.

Also drops the dead nginx.conf.j2 and the network role, both superseded by the
shared includes, and moves .env into the role's templates/ as tandoor.env.j2,
rendered at mode 0600 and read through EnvironmentFile=.

tandoor/playbook.yml

@@ -1,13 +1,53 @@
-#################################################
-# DO Community Playbooks: Docker
-#################################################
 ---
-- hosts: monoco
-  become: true
+# Tandoor Recipes as a rootless Podman Quadlet unit, behind the shared Caddy
+# unit (see caddy/playbook.yml) and the shared Postgres unit
+# (postgres/playbook.yml).
+#
+# Connects as the container user and runs everything as that user: the Quadlet
+# units belong to it, so the connection's PAM session is what makes
+# `systemctl --user` work without any environment juggling.
+#
+# gather_facts is required: podman_user and the home directory come from the
+# user_id / user_dir facts.
+#
+# The rootless-Podman prerequisites (installing podman, enabling lingering, the
+# low-port sysctl, creating the Quadlet directory) are deliberately NOT applied
+# here. They are the shared task file at caddy/roles/podman/tasks/main.yaml, and
+# a host that has already run caddy/playbook.yml has them:
+#
+#   - name: Rootless Podman prerequisites
+#     ansible.builtin.include_tasks: "{{ playbook_dir }}/../caddy/roles/podman/tasks/main.yaml"
+#
+# The variables this play needs are duplicated at the top of vars/default.yml, so
+# it stands on its own. (Applying the commented include above would also need
+# podman_unprivileged_port_start, which lives in caddy/vars/default.yml.)
+#
+# Run with: ansible-playbook -u tanshu tandoor/playbook.yml
+- name: Deploy Tandoor as a rootless Podman Quadlet
+  hosts: emily
+  gather_facts: true
   vars_files:
     - vars/default.yml
 
+  pre_tasks:
+    # This must happen before the app unit is started, not after: the generated
+    # unit references {{ network_name }}.network, and Quadlet fails *unit
+    # generation* (so `systemctl --user start` reports "unit not found") when a
+    # referenced .network file does not exist yet. The same include writes the
+    # Caddy-side drop-in that attaches Caddy to this network, and the Postgres
+    # attach below needs the network unit to exist as well.
+    #
+    # network_name is a play var, so the include can see it directly.
+    - name: Register Tandoor's network with Caddy
+      ansible.builtin.include_tasks: "{{ playbook_dir }}/../caddy/roles/register/tasks/main.yaml"
+
   roles:
-    - network
+    # Attaches this app's network to the shared Postgres unit, which is what
+    # makes POSTGRES_HOST=db resolve, and owns the "Restart Postgres" handler
+    # that postgres/roles/attach notifies. Runs first so the database is
+    # reachable before the app starts.
+    - postgres
+    # The app: data directories, .env, the Quadlet unit, start + verify.
     - tandoor
+    # Appends this site's block to the shared Caddyfile and reloads Caddy.
     - caddy