Prod: public origin gupi.glitch.university, internal services over HTTP

CORS_ORIGIN defaults to https://gupi.${DOMAIN} (the TLS frontend served by the
proxy); the app still reaches Postgres/MinIO by their docker hostnames over
plain HTTP on the shared network. Clarify the split in .env.prod.example and
fix the deploy success URL.

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

docker-compose.prod.yml

@@ -8,8 +8,10 @@ services:
     environment:
       NODE_ENV: production
       PORT: 8787
+      # Internal: reach gu_common services by their docker hostnames over plain HTTP.
       DATABASE_URL: postgres://${POSTGRES_USER}:${POSTGRES_PASSWORD}@gnommo-db:5432/${POSTGRES_DB}
-      CORS_ORIGIN: https://osint.${DOMAIN}
+      # Public: the frontend is served over TLS at gupi.glitch.university by the proxy.
+      CORS_ORIGIN: ${CORS_ORIGIN:-https://gupi.${DOMAIN}}
       JWT_SECRET: ${JWT_SECRET}
       LEVEL_EDITING_ENABLED: ${LEVEL_EDITING_ENABLED:-false}
       MAX_DOCUMENT_BYTES: ${MAX_DOCUMENT_BYTES:-26214400}