B2: per-fact persona opinion layer on /s/[slug]

On the subject fact-node page (/s/[slug]), show per-fact persona opinion signals. Each rated fact should display which persona(s) weight it and by how much — e.g. "Capacity (ml): Chef Persona weights this 0.8×". Requires: (a) an anon-safe aggregate RPC over the ratings table (currently admin-only), (b) persona_slug → display name mapping, (c) UI slot in the fact row DL without polluting the fact-first layout. Data path is TBD (G1 — ratings table is not anon-readable today). Deferred from public-surface build-out (2026-06-14, commit 061239c0).