Auto-calculate deposit line items on invoices

Description: When invoicing a deposit, I have to manually calculate the 50% and edit line items myself. It's easy to get wrong and confusing for the customer to read on their end too.

Use Case: A built-in "deposit %" option on invoices/quotes that auto-generates the correct line item (e.g., "50% Deposit — $X") would remove the manual math and make the invoice clearer for both of us.