Compute the Stripe Connect three-way split for one charge.
Returns what the buyer pays, what Stripe takes, what the platform nets (its
application fee), and what the connected seller nets — plus the platform's
effective take rate. fee_bearer: 'seller' | 'platform' | 'buyer' (who absorbs the
Stripe processing fee). Rates are editable; defaults are US card standard 2.9%+$0.30.
Connector