Fixed mixed inclusion/exclusion projection that caused error:
"Cannot do inclusion on field bills.proofOfPayment.uploadedAt in exclusion projection"
Changed projection to use exclusion-only:
- Exclude bills.attachment (not needed in upload context)
- Exclude bills.proofOfPayment.fileContentsBase64 (large file data)
- Include all other fields implicitly (including uploadedAt for existence check)
This reduces data transfer while maintaining MongoDB projection compatibility.
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Co-Authored-By: Claude <noreply@anthropic.com>
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