Adds users.can_cover_l1, accounts.l1_seats_purchased, subscriptions.l1_seat_limit,
audit_logs.acting_as. Rotates the users.account_role CHECK constraint to include
'l1_tech' (was: 'owner', 'admin', 'engineer', 'viewer').
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
