Fix slave PGDATA permissions: set 700 and postgres ownership before basebackup

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker/pgsql/init-slave.sh

@@ -11,6 +11,8 @@ chown postgres:postgres /tmp/.pgpass
 chmod 600 /tmp/.pgpass
 
 rm -rf "$PGDATA"/*
+chown postgres:postgres "$PGDATA"
+chmod 700 "$PGDATA"
 su-exec postgres env PGPASSFILE=/tmp/.pgpass pg_basebackup -h db-master -D "$PGDATA" -U replicator -Fp -Xs -P -R
 
 echo "hot_standby = on" >> "$PGDATA/postgresql.conf"