feat(infra): redundant GLAuth pair for FallbackServers failover drills

Two local glauth containers (zb-ldap-primary :3893 / zb-ldap-backup :3894)
simulating the NAM two-DC topology, so the primary can be killed during a
drill without touching the shared 10.100.0.35 instance. Drill recipe +
verified-PASS record (HistorianGateway, 2026-08-13) in the README.

infra/glauth-redundant/docker-compose.yml

@@ -0,0 +1,36 @@
+# Redundant LDAP test pair — two GLAuth instances simulating a primary + backup DC,
+# for exercising ZB.MOM.WW.Auth.Ldap 0.2.x `FallbackServers` sticky failover.
+#
+# Runs LOCALLY on the dev Mac (not on 10.100.0.35) precisely so the "primary DC"
+# can be stopped/started during a failover drill without touching the shared
+# zb-shared-glauth that every other dev stack authenticates against.
+#
+# Both instances mount the SAME config.toml — identical directory contents, like a
+# real replicated DC pair. The config is a copy of ../glauth/config.toml with ONE
+# difference: the serviceaccount password here is the well-known local-dev value
+# `serviceaccount123` (the shared instance's is rotated out-of-band, SEC-36).
+#
+#   primary : ldap://localhost:3893   (containers reach it at host.docker.internal:3893)
+#   backup  : ldap://localhost:3894   (containers reach it at host.docker.internal:3894)
+#
+# Drill:  docker stop zb-ldap-primary   → logins fail over to the backup (sticky)
+#         docker start zb-ldap-primary  → preference STAYS on the backup by design
+#         docker stop zb-ldap-backup    → next login walks back to the primary
+name: zb-ldap-redundant
+services:
+  ldap-primary:
+    image: glauth/glauth:latest
+    container_name: zb-ldap-primary
+    restart: unless-stopped
+    ports:
+      - "3893:3893"
+    volumes:
+      - ./config.toml:/app/config/config.cfg:ro
+  ldap-backup:
+    image: glauth/glauth:latest
+    container_name: zb-ldap-backup
+    restart: unless-stopped
+    ports:
+      - "3894:3893"
+    volumes:
+      - ./config.toml:/app/config/config.cfg:ro