feat(delivery): phase 12 — the container, and the defect only a proxy could find

PLAN.md §13 phase 12, the last one. Four decisions of record, D54–D57, taking the
count to fifty-seven; recorded in §6, "How phase 12 delivered it".

A two-stage Dockerfile, a pull-only docker-compose.yml carrying both bind mounts,
.env.example, the workflow that publishes and deploys, CONTRIBUTING.md, the
community-health files this was the only repository of the ten to lack, and
DEPLOY.md.

D54 — a merge deploys, amending D6. build-image.yml pushes
runicgateway-site:latest and :sha-<7>, then rolls the container over on the
`rgcom` runner out of /opt/runicgateway.com, and waits for the container's own
healthcheck rather than for `up -d` to return.

D55 — the site runs on its own host behind a generic reverse proxy, so DEPLOY.md
states the four requirements rather than one worked example, and the container
binds 127.0.0.1 so the safe configuration is the default.

D56 — @astrojs/node derives the request protocol from req.socket.encrypted and
never reads x-forwarded-proto, so behind a TLS-terminating proxy the browser sends
Origin: https://… while the container computes http://… and Astro's CSRF check
compares them for equality. Every beta signup, from every visitor, was answered
403. serve.mjs now normalises both forwarded headers, unconditionally — the image
should deploy and work. Two assertions in test/headers.test.mjs hold both halves.

D57 — DEPLOY.md rather than a README section; SECURITY.md and CODE_OF_CONDUCT.md
are pointers to the org's copies rather than copies, because a copy would hard-code
the contact address D13 confines to brand.json.

Verified: npm run verify green (eleven checks, 36 unit tests, 7 served tests,
astro check 0 errors). The image was built and run with both mounts — a mounted
brand reached 51 files and all 50 search pages, /brand/* fell back per file, a
proxy-shaped signup reached the store, and the export CLI wrote both Play files to
the host mount. docker compose config caught a YAML trap in the healthcheck: a
block sequence reads the `: ` in `r.ok ? 0 : 1` as a mapping.

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

CODE_OF_CONDUCT.md

@@ -0,0 +1,17 @@
+# Code of Conduct
+
+This repository is covered by the Runic Gateway organisation's Code of Conduct — the Contributor
+Covenant, v2.1 — which applies identically across all ten repositories:
+
+**[RunicGateway/docs → CODE_OF_CONDUCT.md](https://gitea.whitlocktech.com/RunicGateway/docs/src/branch/main/CODE_OF_CONDUCT.md)**
+
+It covers the standards expected of everyone taking part, the scope (project spaces and public
+spaces where somebody represents the project), the enforcement guidelines, and **how to report
+unacceptable behaviour privately**.
+
+Reporting goes to the organisation maintainer. That document carries the address; this file
+deliberately does not, for the same reason [SECURITY.md](SECURITY.md) does not — **D13** (`PLAN.md`
+§5) keeps the published contact address in one bind-mounted file so that changing it costs a file
+copy rather than a commit in ten repositories.
+
+Reports are handled privately, and the reporter's identity is not shared with the person reported.