fix: never render 'data warming up' on healthy products

[Flotapponnier]

Two causes of the 'awaiting / data warming up' rows seen on /products/hyperliquid today:

1. Signed metrics: hasData used p50 > 0, but perp-funding can be legitimately negative (Polymarket ETH funding is -0.4 bps right now: longs get paid). 0 stays the worker's no-data sentinel; negative is real data. Changed to !== 0 on products, answers, chain pages, share-card, compare.
2. Degraded store reads: a transient srh/snapshot failure mid-render produced a page where every appearance lost its rank, and ISR cached that broken render for 5 minutes. New tripwire throws when a provider with 3+ appearances has zero ranks anywhere, so revalidation fails and Vercel keeps serving the last good render.