赵月辉 / fastgpt-migrated

The schema-detection aggregate in exportAll builds its $match from teamId
(returned by authDataset as a string). find() casts the string to ObjectId,
but aggregate() does not schema-cast $match values, so the aggregation
matched zero documents. exportSchema became undefined, indexCount/hasMetadata
fell back to 0/false, and the CSV header collapsed to q,a.

Wrap teamId and dataset _ids in Types.ObjectId so the aggregate $match works.
dataset _ids are already ObjectId from .lean(), so that wrap is defensive.

Co-authored-by: Claude <noreply@anthropic.com>