fix: pass site base url to backend container

docs/deployment.md

@@ -10,7 +10,7 @@ Required production changes:
 - set a strong random `DJANGO_SECRET_KEY`;
 - set `DJANGO_ALLOWED_HOSTS` to the real public hostnames only;
 - set `DJANGO_CSRF_TRUSTED_ORIGINS` to the real public HTTPS origins;
-- set `SITE_BASE_URL` to the real public HTTPS base URL used for confirmation emails and QR/check-in links;
+- set `SITE_BASE_URL` to one real public HTTPS base URL used for confirmation emails and QR/check-in links;
 - replace the console email backend with real SMTP settings and a valid sender address;
 - publish only nginx and terminate HTTPS at nginx or a trusted upstream reverse proxy;
 - keep `collectstatic --noinput` in the deployment flow before `up -d`;
@@ -134,6 +134,7 @@ Local Docker convention:
 
 - use nginx as the public entrypoint at `http://localhost`;
 - set `SITE_BASE_URL=http://localhost`;
+- keep `SITE_BASE_URL` as a single URL value, never a comma-separated list;
 - keep `DJANGO_CSRF_TRUSTED_ORIGINS` and browser-facing `CORS_ALLOWED_ORIGINS` aligned with that public URL;
 - if you publish nginx on a different port, update `SITE_BASE_URL` and trusted origins to the same host and port.
 - local/debug reservation email sends also log the confirmation URL so browser testing can continue even if SMTP is missing or fails.

infra/docker/compose.yml

@@ -10,6 +10,7 @@ services:
       DJANGO_CSRF_TRUSTED_ORIGINS: ${DJANGO_CSRF_TRUSTED_ORIGINS}
       DJANGO_DEBUG: ${DJANGO_DEBUG:-false}
       CORS_ALLOWED_ORIGINS: ${CORS_ALLOWED_ORIGINS}
+      SITE_BASE_URL: ${SITE_BASE_URL}
       TIME_ZONE: ${TIME_ZONE:-Europe/Rome}
       DATABASE_URL: ${DATABASE_URL}
       POSTGRES_DB: ${POSTGRES_DB}