Cash account: interest income and expense costs (fees, margin, taxes) that affect performance

Today the Cash Account supports three transaction types: Deposit, Withdrawal, and Interest (rate based). Two gaps come up for users who run a real brokerage cash balance:

1. Interest income. There is no clean way to record the actual interest a broker pays on a cash balance as a return-positive inflow. The Interest type is rate based (you set a percentage and the app estimates accrual), while a Deposit is treated as external capital added, which understates your return. Users want to enter the real interest amounts and have them count as income.

2. Costs: margin interest, advisor fees, and taxes. There is no expense type. Entering these as Withdrawals keeps the cash balance correct but treats them as money moved out rather than a cost, so they do not show as a drag on performance. Users want these to reduce their return the way a real cost does.

Requested:
- Dedicated cash transaction types for income received and for costs (fee, margin interest, tax) that flow through to the performance and return figures, not just the cash balance.
- Bulk CSV import support for those types (the Import Data cash section already handles Deposit / Withdrawal / Interest).

Raised by a user managing a manually tracked brokerage cash account (support ticket #170).