Bulk archive segments

Archive up to 50 segments in one request by setting status: archived. Deliberately DIVERGES from DELETE /v1/segments/{id}: the single-segment DELETE permanently removes the segment (sets deleted: true behind a SEGMENT_IN_USE impact gate, dropping it out of every referencing audience's composition), while bulk archive only changes status — archived segments remain fully resolvable by audiences that reference them, so composition integrity is preserved and no impact gate is needed. Fully reversible via PATCH {status: active} (single or bulk). Best-effort per segment: not-found/deleted ids are reported in the failed array; already-archived segments count as success (idempotent). Requires 'creator' scope.