chore(auth): ScadaBridge unify dev LDAP base DN to dc=zb,dc=local (Task 1.6)

Replace dc=scadabridge,dc=local with dc=zb,dc=local in all dev/test LDAP
references — app config, docker test-cluster node configs (docker/ and
docker-env2/), GLAuth fixture, dev tooling, Host.Tests fixtures,
IntegrationTests factory, and operational test_infra docs. OU structure
(ou=SCADA-Admins,ou=users,etc.) preserved throughout. Email domains
(@scadabridge.local), hostnames, and container names are untouched.
Historical plan docs (2026-05-24-second-environment.md,
2026-05-31-folder-repo-rename-scadabridge-design.md) excluded as
point-in-time records. No synthetic dc=example,dc=com placeholders touched.

docker-env2/central-node-b/appsettings.Central.json

@@ -27,8 +27,8 @@
         "Port": 3893,
         "Transport": "None",
         "AllowInsecure": true,
-        "SearchBase": "dc=scadabridge,dc=local",
-        "ServiceAccountDn": "cn=admin,dc=scadabridge,dc=local",
+        "SearchBase": "dc=zb,dc=local",
+        "ServiceAccountDn": "cn=admin,dc=zb,dc=local",
         "ServiceAccountPassword": "password"
       },
       "JwtSigningKey": "scadabridge-env2-dev-jwt-signing-key-must-be-at-least-32-characters-long",