Retain last known cost price when no distributor is linked

Description:

When a product has no active distributor link, the cost price currently shows as 0, leaving users with no pricing reference when building a quote. We would like Salesbuildr to fall back to the last known cost price in this situation, so there is always a meaningful starting point visible.

Why:

We work with suppliers whose price lists are not automatically imported. When no distributor is linked, we lose visibility of the cost price entirely. Having the last known price shown by default would significantly reduce manual lookup time and keep quotes accurate even when distributor data is missing.