feat(deploy): bake the ServerCluster/ClusterNode seed into docker-compose

Adds a one-shot cluster-seed service to docker-dev/docker-compose.yml
that pre-populates the three Akka clusters' scope rows in the shared
OtOpcUa ConfigDb so operators don't have to click through /clusters +
/hosts on every fresh bring-up.

Seed contents:
  ServerCluster   MAIN (Warm/2), SITE-A (Warm/2), SITE-B (Warm/2)
  ClusterNode     driver-a + driver-b  → MAIN
                  site-a-1 + site-a-2  → SITE-A
                  site-b-1 + site-b-2  → SITE-B

NodeCount + RedundancyMode honour the CK_ServerCluster check constraint.
ApplicationUri follows the urn:OtOpcUa:<NodeId> convention; uniqueness
across the fleet satisfies UX_ClusterNode_ApplicationUri.

Mechanism:
  - docker-dev/seed/seed-clusters.sql — idempotent INSERTs (IF NOT EXISTS
    guards on every row).
  - docker-dev/seed/entrypoint.sh — bash wrapper that waits for SQL to
    accept connections, then polls until dbo.ServerCluster exists (the
    host containers' EF auto-migration creates it on first boot), then
    applies the SQL script.
  - cluster-seed service uses mcr.microsoft.com/mssql-tools as the base
    image (bash + sqlcmd available), restart: "no" so it runs once.

Re-running `docker compose up` is safe: the seed exits cleanly on the
second run because every INSERT is guarded.

Manual re-seed: `docker compose run --rm cluster-seed`.

docker-dev/docker-compose.yml

@@ -57,6 +57,20 @@ services:
       timeout: 5s
       retries: 20
 
+  # ── Cluster seed (one-shot) ────────────────────────────────────────────────
+  # Waits for SQL + the host containers' EF auto-migration, then INSERTs the
+  # three ServerCluster rows and the six ClusterNode rows that scope each Akka
+  # mesh inside the shared OtOpcUa ConfigDb. Idempotent — re-runs are no-ops.
+  cluster-seed:
+    image: mcr.microsoft.com/mssql-tools:latest
+    depends_on:
+      sql:
+        condition: service_healthy
+    volumes:
+      - ./seed:/seed:ro
+    entrypoint: ["/bin/bash", "/seed/entrypoint.sh"]
+    restart: "no"
+
   ldap:
     image: bitnami/openldap:2.6
     environment: