Search documents by filename using full-text search.
request.filters accepts the same operator set as /retrieve/chunks: $eq, $ne, $gt, $gte, $lt,
$lte, $in, $nin, $exists, $type, $regex (with optional i flag), $contains, and the logical
operators $and, $or, $nor, $not. Comparison clauses honor typed metadata (number, decimal,
datetime, date).