Get aggregated Product / Variant details for a bulk selection

Accepts either explicit record ids (items, up to 50000) or the current products search (query). Ids are loaded from the database in chunks with a field projection. Select All must send query (the same body as POST /products/search). Optional recordState (draft or published) forces that catalog layer: Has published reads each record's live snapshot and Has draft reads the working copy, even when stored listingStatus values differ. Without recordState, the layer is inferred from the documents and mixed Draft/Published statuses are rejected. Same values become state=common; differing or partially empty values become state=multiple; all-empty becomes state=empty. Missing/deleted ids are listed in selection.missing. Incompatible mixed contexts are rejected. Published aggregation uses each record's live snapshot and is read-only.