[Regression] Negative price values blocked on quotes — validation over-applied from setup price to all fields

After a recent release, negative price values are no longer accepted on any quote line item field. The validation that was originally scoped to setup price only has been expanded to all price fields (unit price, extended price, etc.). Entering a negative value triggers a validation error and blocks saving the quote.

This is a regression — negative values were previously allowed and are a valid business use case (discounts, credits, adjustments). Autotask itself still accepts negative values on its side, so the restriction is Salesbuildr-only.