venus telemetry PG: no owned schema convention — role/table/view per host (lezama/venus/whey), unify + add prune mechanism

Elazar 2026-08-23: telemetry_whey_rw / telemetry_ro naming implies a whey-specific role pattern that was never extended to lezama or venus — suspect unorganized tables fleet-wide with no prune mechanism. Scope: audit all tables/views/roles in venus's telemetry PG (usage.*, v_latest.*, whatever else exists), design one consistent per-host role+table+view convention (lezama/venus/whey), and add retention/pruning where none exists. Also surfaces the immediate gap: no registered maintainer existed for the venus PG instance itself (only individual writer scripts were registered) — nw-venus-cc accepting that seat now, in own words, per fleet no-inference-seat rule.