postgres-init: enable citext extension on asxpio db

Needed for case-insensitive email columns in the asxpio users table.
Runs as the Postgres superuser inside the init container; idempotent.

init/postgres-init.sh

@@ -23,7 +23,14 @@ ensure_db() {
   fi
 }
 
+ensure_extension() {
+  db="$1"
+  ext="$2"
+  psql -d "${db}" -c "CREATE EXTENSION IF NOT EXISTS \"${ext}\";"
+}
+
 ensure_role "asxpio" "${ASXPIO_DB_PASSWORD}"
 ensure_db   "asxpio" "asxpio"
+ensure_extension "asxpio" "citext"
 
 echo "postgres-init: done"