Containerise: Dockerfile, Compose stack and wildcard TLS

One server now, the same image and env vars for many later: point
DJANGO_DATABASE_URL / DJANGO_REDIS_URL at central services, set a bucket, drop the
db and redis services, run several web containers behind a load balancer. No code
changes.

The wildcard certificate is what shapes this. Subdomain tenancy needs
*.rosterchief.app, and Let's Encrypt will not issue a wildcard over HTTP-01 -- only
DNS-01 -- so Caddy is built with a DNS provider plugin and needs an API token. That
single constraint is why the proxy is Caddy rather than the usual nginx+certbot.

The image apt-installs libpango and friends, which is what WeasyPrint binds to. The
PDF invoices that cannot render on a Mac without Homebrew work in the container by
construction.

Migrations are NOT run by the entrypoint: with more than one web container they
would race, and a starting gunicorn worker is a bad place to discover a failed
migration. Deploy runs them once, explicitly.

Two things the local build check caught, either of which would have failed the
image build at collectstatic (manifest storage treats a missing referenced file as
fatal):

- chart.js ended with a sourceMappingURL pointing at a .map we never vendored.
  Stripped, with an npm script so re-vendoring cannot bring it back.
- The Tailwind INPUT file lived at static/src/app.css, inside the served static
  tree, so collectstatic collected it and then choked on its @import "tailwindcss".
  It belongs outside: it is a build input, not an asset. Now assets/app.css.

Verified locally under gunicorn + WhiteNoise + manifest storage: pages serve and
the CSS comes back hashed. The image itself is unverified -- there is no container
runtime on this machine.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.env.compose.example

@@ -0,0 +1,10 @@
+# Copy to .env — read by docker compose itself (not by Django).
+ROSTERCHIEF_BASE_DOMAIN=rosterchief.app
+ACME_EMAIL=you@example.com
+
+# DNS-01 is the only way to get the *.rosterchief.app wildcard. Token needs DNS:Edit on the zone.
+CLOUDFLARE_API_TOKEN=
+
+POSTGRES_DB=rosterchief
+POSTGRES_USER=rosterchief
+POSTGRES_PASSWORD=