Issue #3595227: Full-UI French via Gettext (drush locale:update broken on Tugboat); drop dead auto-rebuild key

Fixes the full-UI French on the demo, which never arrived: drush locale:check / locale:update are broken on the Tugboat dev-core image (LocaleFetch::batchVersionCheck not found; _locale_translation_default_update_options() undefined), and the build "|| true" hid it.

Changes:

• Replace the broken drush commands with a synchronous fetch + Gettext::fileToDatabase import in setup.php. Core resolves each project l.d.o .po URL; missing ones 404 and are skipped; core/contrib import as community strings so pdv customized strings are untouched.
• Drop the dead auto-rebuild config.yml key: not a valid Tugboat config property (schema root only accepts services). Periodic base rebuilds are a dashboard setting (base already rebuilds nightly ~00:00 UTC).

Verified on this MR preview (gate temporarily opened to mergerequest): Drupal rendered fully French. Gate is now back to base-only (type = branch), so this MR preview rebuilds English; full French lands on the base 1.x preview after merge.