Adds the commercial Oban Pro package (vendored from the towerops-web2
vendor tree) so this project can use its workers, plugins, and
Smart engine features.
Vendor oban_web 2.12.1 and oban_met 1.1.0 (taken from the
towerops-web2 vendor tree), bump oban to ~> 2.21, and mount the Oban
dashboard at /admin/oban behind the existing require_admin on_mount
hook. Adds an admin-only "Oban" nav link and extends the Dockerfile
to copy vendor/ before deps.get so production builds pick up the
path dependencies.
