#2958 data query: no fallback from spec name to data instance name

Gap

swamp data get --workflow falls back to the specName tag when no item has the exact data name, so asking for classification finds an item stored as classification-main. data query matches name exactly; callers must know to use specName == 'classification' instead.

Expected

Either a documented, ergonomic way to match by instance name or spec name in one predicate, or guidance in the query docs and errors that points users from name to specName when nothing matches.

Context: swamp data get is being deprecated in favor of swamp data query (follow-up to swamp-club#2948, where data get --workflow silently returns an arbitrary step's data when several steps share a data name). This closes one gap that data query has compared with data get.