chore: retire the per-client domain setup (plan step 9); addresses → bonamin.net

- remove setup-ssl.sh (mkcert IP certs) - superseded by install.sh's
  self-signed cert and the backend-managed TLS identity
- manager: "Waiter Domain (παλιό σύστημα)" - shown only for sites that
  still have one
- .env.example: REGISTRY=registry.bonamin.net and
  CLOUD_URL=https://xenia-api.bonamin.net (it pointed at the admin panel,
  xenia-admin, even before the domain move); install.sh points to the
  sysadmin panel at xenia-admin.bonamin.net
- pack README registry example updated
Proxy config unchanged (HTTPS domain blocks stay so not-yet-migrated sites
keep working until their visit).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/README.md

@@ -101,7 +101,7 @@ cd waiter_pwa; npm run lint
 
 # Build release images (VERSION comes from .env). See the parent's DEPLOYMENT_GUIDE.md.
 docker compose -f docker-compose.yml -f docker-compose.dev.yml build
-docker push registry.bonamin.gr/pos-backend:<ver>   # + pos-waiter, pos-manager
+docker push registry.bonamin.net/pos-backend:<ver>   # + pos-waiter, pos-manager
 ```
 
 ## Native Android app (waiter_pwa)