Find duplicate feature requests

Returns previously computed duplicate groups for the project's feature requests from a cache; { groups: [] } when nothing is cached yet. Pass ?force=true (or { "force": true } in the body) to run a fresh AI scan; results are cached for 24 hours. The scan covers up to 2000 active feature requests; archived, hidden, spam, already-merged and DONE tickets are excluded. The project header is required.