fix(docker-dev): self-bootstrap schema via one-shot migrator (fixes fresh-volume quirks)

Adds a 'migrator' Dockerfile stage + Compose service that runs 'dotnet ef
database update' once on bring-up, so a fresh SQL volume gets the schema with no
operator step (quirk 1). cluster-seed + every host node depend on it via
service_completed_successfully, so the seed never races an in-progress migration
(quirk 2). Host build pinned to target: runtime (the migrator is now the last
stage). entrypoint + README updated; the manual 'dotnet ef' first-time step is
gone. Verified: down -v + up --build self-bootstraps (migrator+seed exit 0,
6 nodes up), deploy Sealed 6/6.

docker-dev/seed/entrypoint.sh

@@ -1,20 +1,13 @@
 #!/usr/bin/env bash
-# docker-dev cluster-seed entrypoint. Waits for the OtOpcUa ConfigDb schema to
-# be in place, then applies the idempotent row seed.
+# docker-dev cluster-seed entrypoint. Applies the idempotent row seed.
 #
-# IMPORTANT: this container does NOT run EF migrations — sqlcmd can't execute
-# the V2 migration script cleanly because it contains CREATE PROCEDURE
-# statements inside IF NOT EXISTS BEGIN ... END blocks (procs must be the
-# first statement in their batch). Migrations are owned by the operator:
-#
-#     dotnet ef database update \
-#         --project src/Core/ZB.MOM.WW.OtOpcUa.Configuration \
-#         --startup-project src/Server/ZB.MOM.WW.OtOpcUa.Host
-#
-# (with ConnectionStrings__ConfigDb pointing at Server=localhost,14330;...).
-# Once the schema is in place, restart the cluster-seed container — or just
-# `docker compose up -d` and the seed will pick up where it left off thanks to
-# the IF NOT EXISTS guards in seed-clusters.sql.
+# This container does NOT run EF migrations — sqlcmd can't execute the migration
+# script cleanly (it has CREATE PROCEDURE inside IF NOT EXISTS BEGIN ... END
+# blocks; procs must be the first statement in their batch). The schema is owned
+# by the `migrator` Compose service (dotnet ef), which this seed depends on via
+# `service_completed_successfully` — so by the time we run, migrations are fully
+# applied. The dbo.ServerCluster wait below is therefore just a fast sanity check.
+# Re-runs are safe: every insert in seed-clusters.sql is IF NOT EXISTS-guarded.
 
 set -euo pipefail
 
@@ -37,7 +30,7 @@ until run_sql_in master -Q "SELECT 1" >/dev/null 2>&1; do
 done
 echo "[cluster-seed] SQL Server up."
 
-echo "[cluster-seed] waiting for ${DB} database + dbo.ServerCluster table (operator must run dotnet ef database update)..."
+echo "[cluster-seed] verifying ${DB} schema (dbo.ServerCluster) is present (migrator should have applied it)..."
 until run_sql_in "$DB" -Q "IF OBJECT_ID('dbo.ServerCluster') IS NULL THROW 50001, 'missing', 1; SELECT 1" >/dev/null 2>&1; do
     sleep 3
 done