ZEROHAND CSV Preflight Samples
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1. clean.csv
   Expected: no missing required values and no duplicate email.

2. missing-required.csv
   Mark email as Required. Expected: FAIL on the blank email row.

3. duplicate.csv
   Mark email as Unique. Expected: WARN on the second a@example.com row.

4. malformed-duplicate-header.csv
   Expected: reject because the header name "email" appears twice.

These files contain synthetic sample data only.
