spp_api_v2: GET /Group?type= is documented and accepted but never applied #565

Problem

GET /Group accepts a type query parameter (household/family/organization/other), documented in the router
docstring and passed into the search params (spp_api_v2/routers/group.py, ~187), but
SearchService.search_groups() never reads it. ?type=household returns every group.

PR #555 (#554 item H) made the other search filters fail closed; this one was left out because fixing it means
implementing the filter.

Proposal

Implement the filter (map to the group-type field/vocabulary; unknown type → empty result, malformed → 400, like the
other filters), or remove the parameter from the endpoint and docs.