Could you please add an API to get the current transferable balance value

During the settlement and transfer of the ore pool, an error will be reported if the transferable balance is insufficient. It cannot be judged that the transferable balance is insufficient before the start, which will cause some inconvenience

No file, test, endpoint, or entry point is named. Start by locating the existing settlement and ore-pool transfer API paths, then determine how transferable balance is calculated and exposed. Done means callers can obtain the current transferable balance before a transfer and the behavior is covered by tests.

Written by the indexing model from the issue text.