feat(deploy): sync schema to replication subscribers before migrating

Logical replication carries rows but not DDL, so a migration that adds a
column stalls every subscriber with "missing replicated columns" until the
column exists there too. _prisma_migrations is replicated, so migrate deploy
on a subscriber reports nothing pending while its tables lag behind.

sync-replica-schema.sh applies pending migrations to each subscriber first,
tracking them locally in _replica_ddl_applied, then migrates the publisher.
--check reports subscription state and columns missing on any replica.

Co-authored-by: Cursor <cursoragent@cursor.com>

deploy/replicas.env.example

@@ -0,0 +1,6 @@
+# Copy to deploy/replicas.env on the publisher host (gitignored — holds passwords).
+#
+# Every logical-replication subscriber of superadmin_pub, space/comma/newline separated.
+# The user must be able to run ALTER TABLE (table owner or superuser).
+REPLICA_DSNS="postgresql://USER:PASSWORD@SLAVE_1_IP:5433/superadmin
+postgresql://USER:PASSWORD@SLAVE_2_IP:5432/superadmin"