feat: support split Dashboard and API origins (ADR 0045)

An installation can now serve the Dashboard and the API on sibling
hostnames (dash./api.) beside the default same-origin topology, from one
image and with configuration alone.

- The Dashboard learns its API origin at run time: the built page carries
  one empty <meta name="ekklesia-api-origin">, which the API fills with its
  identity base URL's origin at startup, before computing the page's ETag.
  The shell accepts only a canonical http(s) origin and otherwise fails
  closed without making a request. The build-time EKKLESIA_API_BASE_URL is
  gone from the bundle; the development server injects the same element.
- The display host stays on the API's origin, so its device cookies,
  requests, and offline cache are unchanged.
- The API trusts its own origin (trusted origins plus the identity base
  URL), as Better Auth already does, so the display page's mutations pass
  the origin check without operators listing it.
- Doctor validates EKKLESIA_DASHBOARD_ORIGIN exactly as the API's startup
  does (it previously skipped it), reports the topology without printing
  hostnames, and warns when split hostnames are not siblings.
- The module UI contract states the CORS header limit (safelisted headers
  plus Content-Type, safelisted response headers only).
- Reference deployment: Caddyfile.split.example (Dashboard hostname serves
  / and its script; API hostname serves /api/*, /display/*, and the
  display script; each refuses the other's paths) and
  EKKLESIA_DASHBOARD_HOSTNAME in the proxy overlay and env examples.
- The deploy smoke test runs either topology (CI runs both). The split run
  installs the module template as a test-only module, checks per-hostname
  routing and exact CORS, then drives a digest-pinned headless Chromium
  over the DevTools protocol, with no added dependency: sign-in on the
  Dashboard hostname, the session cookie host-only on the API hostname,
  the module UI imported cross-origin and its credentialed request
  succeeding, the display and its service worker on the API hostname, and
  sign-out.

ADR 0045 is marked Accepted.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

deploy/env/compose.env.example

@@ -10,9 +10,14 @@ EKKLESIA_ENV_DIR=/etc/ekklesia
 EKKLESIA_TLS_DIR=/etc/ekklesia/tls
 
 # --- compose.proxy.yaml ---------------------------------------------------------------------------
-# The Ekklesia hostname (Dashboard, API, displays) and the storage hostname (signed object URLs).
+# The Ekklesia hostname and the storage hostname (signed object URLs). In the default same-origin
+# topology (Caddyfile.example) EKKLESIA_HOSTNAME serves the Dashboard, the API, and displays.
 EKKLESIA_HOSTNAME=
 EKKLESIA_STORAGE_HOSTNAME=
+# The split topology only (ADR 0045, Caddyfile.split.example): the Dashboard's own hostname, while
+# EKKLESIA_HOSTNAME is the API's and the displays'. Both must share one registrable domain, for
+# example dash.example.org and api.example.org. Leave empty for the same-origin topology.
+EKKLESIA_DASHBOARD_HOSTNAME=
 # Contact address for the ACME account (certificate expiry notices).
 EKKLESIA_ACME_EMAIL=
 # EKKLESIA_CADDYFILE=./Caddyfile

deploy/env/ekklesia.env.example

@@ -23,15 +23,19 @@ EKKLESIA_DATABASE_TLS_MODE=verify-full
 # scripts/init-tls.sh prints this exact line. It is the only CA the database connection trusts.
 EKKLESIA_DATABASE_CA=
 
-# --- Identity (ADR 0011, ADR 0018, ADR 0034) ----------------------------------------------------
-# The public https origin of the Ekklesia hostname, with no path. Production rejects http and
-# loopback origins.
+# --- Identity (ADR 0011, ADR 0018, ADR 0034, ADR 0045) -----------------------------------------
+# The public https origin of the API, with no path: the Ekklesia hostname in the same-origin
+# topology, the API's hostname in the split one. Production rejects http and loopback origins.
 EKKLESIA_IDENTITY_BASE_URL=
-# Comma-separated exact origins allowed to make credentialed requests. Normally just the base URL.
+# Comma-separated exact origins allowed to make credentialed requests. The API's own origin is
+# always trusted and need not be listed. Same-origin topology: the base URL. Split topology: the
+# Dashboard's origin.
 EKKLESIA_IDENTITY_TRUSTED_ORIGINS=
 # At least 32 random characters. Rotating it signs every user out.
 EKKLESIA_IDENTITY_SECRET=
-# Leave unset: the Dashboard is served from the base URL (ADR 0044).
+# Same-origin topology: leave unset; the Dashboard is served from the base URL (ADR 0044).
+# Split topology: the Dashboard's https origin, which must also be in the trusted origins. Emailed
+# verification and reset links land here (ADR 0045).
 # EKKLESIA_DASHBOARD_ORIGIN=
 # Production refuses public sign-up. Leave unset.
 # EKKLESIA_PUBLIC_SIGNUP_ENABLED=