Replaced broken `association :brand, factory: :captain_brand, account: account`
(FactoryBot cannot evaluate `account` lazily that way) with a transient block
that does `Captain::Brand.find_by(account_id: account.id) || association(...)`,
ensuring the brand always belongs to the same account as the unit.
Adds factory spec (6 examples) confirming standalone create, account override,
and brand reuse all work correctly.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
