Returns a single company by id, including its members, related people,
custom columns and collector account. The company must be one the
authenticated user belongs to (Cardda staff can read any).

The balance_cents and wallets attributes (and the computed balance /
total_allocated_funds) are returned only to users with the balance
permission; other members receive the company without them. User attachment
URLs are included only for users allowed to view them (admins or
companies_manage).