Live probe of every upstream Artery depends on (admin)

Runs a 3s-timeout probe against Polymarket REST, Kalshi REST, Hyperliquid REST, the configured Polygon RPC, Redis, and Postgres in parallel. Returns a `pingMs` + status (`healthy` ≤1s, `degraded` >1s, `down` on probe failure) per provider, plus the `lastSuccessAt` / `lastErrorAt` tracked across probe runs. Result is cached server-side for 30s so page reloads don't hammer upstreams. Audit-logged as `admin.source-health.viewed`. Short bounded list (≤10 providers); no pagination.