feat(deploy): Traefik active-leader routing + docker-dev compose (Task 63)

- scripts/install/traefik.yml + traefik-dynamic.yml: Traefik static + dynamic
  config. One :80 entry point, one router on HostRegexp(otopcua.*), one
  service load-balancing admin-a:9000 + admin-b:9000 with /health/active health
  check (interval 5s, timeout 2s, expected 200). Followers return 503 from
  /health/active so Traefik drops them within the next interval after a
  leadership change.

- scripts/install/Install-Traefik.ps1: downloads Traefik for Windows, drops the
  yml configs, registers the OtOpcUaTraefik Windows service via sc.exe with
  restart-on-failure. Companion to Install-Services.ps1.

- docker-dev/{Dockerfile,docker-compose.yml,traefik-dynamic.yml,README.md}:
  Mac-friendly four-node fleet (admin-a + admin-b + driver-a + driver-b) plus
  SQL Server 2022 + OpenLDAP + Traefik. Single OtOpcUa.Host image built once;
  Compose drives OTOPCUA_ROLES + Cluster:* per container to differentiate the
  four hosts. README walks through bring-up + failover smoke + the dev LDAP
  users.

Note: untested on macOS (no local Docker — see docs/v2/dev-environment.md).

docker-dev/traefik-dynamic.yml

@@ -0,0 +1,21 @@
+# docker-dev companion to scripts/install/traefik-dynamic.yml. Same routing rules,
+# but the upstream targets are the Compose service names (admin-a, admin-b) on
+# port 9000 instead of the Windows hostnames a bare-metal deployment would use.
+
+http:
+  routers:
+    otopcua-admin:
+      entryPoints: ["web"]
+      rule: "PathPrefix(`/`)"
+      service: otopcua-admin
+
+  services:
+    otopcua-admin:
+      loadBalancer:
+        servers:
+          - url: "http://admin-a:9000"
+          - url: "http://admin-b:9000"
+        healthCheck:
+          path: /health/active
+          interval: 5s
+          timeout: 2s