External identifiers are text, not numeric amounts

For GiveCampus constituent data and imports.

Constituent identifiers can contain letters: keep Salesforce and similar IDs as text. The legacy identifier column is text, the person identifier is a string, and these models do not specify a fixed maximum-length validation. That does not guarantee unlimited length in every importer or integration. Preserve the full value and case, review identifier-normalization settings, and test the intended import/API and downstream report before a bulk replacement.