Constituent PUT is not a general partial patch

For GiveCampus integrations and API.

Do not assume omitted fields are preserved by constituent PUT. In v1 and v2, constituent CRM updates use the submitted row, including empty or default values for omitted fields. Blank or omitted affiliations clear existing affiliations. Verify the exact API version and field schema, retain the intended existing values in a supported update payload, and test/read back representative records before bulk updates.