Extract duplicated inline StandaloneDocker attribute arrays in the
Server boot lifecycle into a dedicated method, eliminating repetition
between the root-server (id=0) and normal-server paths.
Also harden the shared_environment_variables migration by wrapping
DDL statements in DB::transaction() and using DROP CONSTRAINT IF EXISTS
to make the migration safely re-runnable.
Add unit test covering the extracted method to verify uuid is always
present in bootstrap attributes.
