Templates: Line item description fields behave inconsistently and persist stale values — redesign to explicit/dynamic model

Description

Template line items currently have two issues with how description fields are handled:

The field labelled "short description" in a template line item incorrectly maps to the "Description in quote" field on the resulting quote. The label is misleading and the mapping is wrong — a simple relabel to "Description in quote" would align it with how the field is named everywhere else in the platform.

Additionally, description values are stored as a snapshot at the time the template is created. If the underlying product changes afterwards, the old value persists on the template and continues to appear on quotes generated from it. Users clearing descriptions in Autotask or on the product level see no effect, because the template is serving its own cached value with no indication that this is happening.

Steps to reproduce

1. Create a template and add a product that has a description value at that point in time

2. Edit the template line item and enter a value in the "short description" field

3. Generate a quote from the template — the value appears in the description field, not the short description field

4. Now update or clear the description on the underlying product

5. Generate a new quote from the same template — the old value still appears

Expected behaviour

1. The field should be correctly labelled "Description in quote" to match the rest of the platform.

2. Template line items should follow the explicit/dynamic model similar to prices: a dynamic field (grayed out) reflects the current product value at quote generation time, while an explicit value entered at template level overrides the product and is always leading. A visual indicator should make it clear to the user when a line item has an explicit override set.

Impact

Users experience stale or misrouted description text on quotes with no way to identify the source. Clearing descriptions in Autotask or Salesbuildr has no visible effect, leading to repeated support contact and manual cleanup on every quote created from a template.