[DwC export]: Implement auto-mapping of Specify fields to DwC terms

[grantfitzsimmons]

Goal

When a field is added to the schema mapping or a default mapping is loaded, automatically pre-populate the Term column based on mappingPath matches in the schema terms JSON.

Background

Auto-mapping reduces manual effort and ensures correctness. Fields whose mappingPath exactly matches a term's entry in the JSON are mapped automatically; unmatched fields are left for the user to map manually.

Acceptance Criteria

• On field add, the system checks the schema terms JSON for a term whose mappingPath matches the field's path.
• If a match is found, the Term column is pre-populated with that term's IRI.
• If no match is found, the Term column is left empty (no auto-mapping applied).
• Auto-mapped terms can be changed or cleared by the user.
• Loading a default mapping pre-populates all matched fields per the JSON (no manual mapping required for defaults).