Set Invoice Parcel Count Route

Put the month's parcel count into an existing per_parcel draft and reprice it from the contract.

Frederick, 2026-08-04: "Iowa is the only thing that remains in draft form... once I fill in the information, the amount of parcels, a send button on it." The billing tick raises that invoice on the 1st with everyone else's, before the count is knowable; this is how the real number gets into it afterwards. Repricing runs through the same derive_contract_billing the generator uses, so the rate and the line wording come from the contract, never from the caller.

CHANGED 2026-10-04 (APPENDED; the quote above is the 2026-08-04 record): Frederick, 2026-10-04: "I don't want to have it wait. Once I put the number, the number parcels in, it should just go out the next business day at 9 a.m. local time." Saving the count now also SCHEDULES the invoice's send; the response carries scheduled_send ("Sends Mon Oct 5, 9:00 AM CT"). The Send button still works and cancels the schedule.