[DwC export]: Allow entering static/verbatim text as a Term value (V2)

[grantfitzsimmons]

Goal

(Planned for V2) Allow users to map a DwC term to a static text value (e.g., "PreservedSpecimen" for basisOfRecord) rather than a Specify field.

Background

Some DwC terms are the same for every record in a collection (e.g., basisOfRecord). Static values avoid the need for a calculated or redundant field. Deferred pending confirmation of IsStatic/StaticValue field addition.

This is useful for cases like the Web Portal, which rely on custom column name values so they are intuitive for those using and searching the portals.

Acceptance Criteria

• A toggle or checkbox on a row switches it to "Static Value" mode.
• In static mode, a text input replaces the field picker; the user types the verbatim value.
• spqueryfield.IsStatic is set to true; StaticValue stores the text.
• Static rows export the literal string for every record.
• Static rows still require a Term to be selected.