C1: per-user picked/discarded counts on /o/[slug]

On the opinionated option page (/o/[slug]), show per-user social proof: "X people picked this" / "Y discarded". Requires a SECURITY DEFINER RPC that aggregates option_reactions by slug across public lists — anon-safe, no per-user attribution. The A2 crowd aggregate (get_crowd_aggregate_for_slug) already aggregates preference_score and reaction weights; this task adds the picked/discarded reaction counts specifically. UI placement: below the verdict chip, above "All picks for this item". Deferred from public-surface build-out (2026-06-14, commit 061239c0).