Resolve names to filter-option ids

Names in, ids out, for one filter field. The talent index stores ids and never names, so anything choosing filter values resolves through here first. Vector-backed fields (skills, designations, colleges, education_degrees, education_fields) return their top candidates; the rest match by text. Every candidate is returned ranked and the caller picks — a name with no candidates comes back with an empty list rather than a guess. Fields whose dropdown offers entity groups (a metro area, an institution family, a discipline) return the matching groups in their own "groups" list with their member count; a group id goes under "groups" in the leaf, never into the id list.