fix(docker-dev): persist dev SQL ConfigDb on a named volume

The docker-dev sql service had no volume, so its data lived in the container
writable layer. A recreate silently dropped the OtOpcUa database and every host
node failed its configdb health check (AdminUI 503) until an operator re-ran
'dotnet ef database update' + the cluster-seed. Add a named volume
(otopcua-mssql-data -> /var/opt/mssql) so the migrated schema + seeded clusters
survive 'docker compose up' cycles.

docker-dev/docker-compose.yml

@@ -51,6 +51,13 @@ services:
       MSSQL_PID: Developer
     ports:
       - "14330:1433"
+    # Persist the ConfigDb across container recreates. Without this the dev SQL
+    # is ephemeral (container writable layer), so a recreate silently drops the
+    # OtOpcUa database and every host node fails its configdb health check until
+    # EF auto-migration + cluster-seed rebuild it. The named volume keeps the
+    # schema + seeded clusters between `docker compose up` cycles.
+    volumes:
+      - otopcua-mssql-data:/var/opt/mssql
     healthcheck:
       test: ["CMD-SHELL", "/opt/mssql-tools18/bin/sqlcmd -S localhost -U sa -P 'OtOpcUa!Dev123' -No -Q 'SELECT 1' || exit 1"]
       interval: 10s
@@ -307,3 +314,7 @@ services:
       - site-a-2
       - site-b-1
       - site-b-2
+
+volumes:
+  # SQL Server data dir — persists the OtOpcUa ConfigDb across container recreates.
+  otopcua-mssql-data: