Map different shipping products in CW to shipping types in SB

Summary
MSP/reseller customers need to map different shipping options in Salesbuildr to different ConnectWise catalog product SKUs. Currently, all shipping methods (Direct Ship, Freight Charges, etc.) push to ConnectWise using a single SKU, regardless of which shipping type was selected on the quote. This prevents accurate product tracking in ConnectWise when different shipping methods require distinct catalog entries.

**Background**
When an MSP creates quotes in Salesbuildr, they define multiple shipping options to reflect different fulfillment methods. These options have different labels, costs, and pricing. Today, when any of these shipping options are pushed to ConnectWise as a line item, they all map to the same ConnectWise product SKU. The shipping label, price, and cost transfer correctly, but the underlying catalog product is identical regardless of shipping method selected.

The customer needs different ConnectWise SKUs for different shipping methods so their product catalog in ConnectWise accurately reflects the shipping method used on each quote.

**What Was Investigated**
Not yet investigated. Further discovery needed on: how many customers require this functionality, whether alternative ConnectWise configurations could address this, and the technical feasibility of supporting per-shipping-method SKU mapping.

**The Gap**
The product supports only one ConnectWise product SKU for all shipping options. There is no UI or configuration that allows users to assign different SKUs to different shipping methods in Salesbuildr.

**Requested Feature**
- Allow users to map each shipping option in Salesbuildr to a distinct ConnectWise product SKU
- Add a configuration field (or section) in the ConnectWise integration settings where users can specify SKU for each shipping option by name
- When a quote with a specific shipping option is pushed to ConnectWise, use the mapped SKU for that shipping method, not a default SKU
- Preserve the existing behavior for shipping label, price, and cost transfer

**Why This Matters**
Without this feature, customers cannot maintain accurate product records in ConnectWise when they use multiple shipping methods. This creates confusion in their product catalog and makes it difficult to track which shipping method was used on historical quotes. It affects any MSP that uses ConnectWise integration and offers more than one shipping option.

**Proposed Priority**
Medium. This is a specific integration use case that affects quote-to-ConnectWise accuracy, but only for customers who require multiple distinct shipping SKUs. Not a core platform blocker.