When project.otp.repo=true: creates the {Module}.Schema/{Module}.Migration base conventions (UUIDv7 primary keys, :utc_datetime_usec timestamps, citext) and a bootstrap citext-enabling migration, for both type=otp and type=web. type=otp projects additionally get {Module}.Repo, wired into the --sup-generated Application's supervision tree, ecto_repos config, and local-Postgres dev/test connection defaults (matching mix phx.new's own convention) -- type=web already gets all of that for free from mix phx.new itself.