fix: static-to-dynamic 500s + thirdweb tripwire

[Flotapponnier]

Summary

• /alternatives/[slug]: revalidate = 60 + fetchPerpCohort() (which uses cache: "no-store) → "Page changed from static to dynamic" for dydx/gains/hyperliquid/polymarket. Fixed with force-dynamic.
• /products/polymarket: same root cause — loadBenchFromBlob("perp-fees-at-size") fires a cache: "no-store" fetch from an ISR page. The bench was already deleted so this always returned null. Removed the call, passing null directly to getPerpVenueContext.
• /products/thirdweb: degraded-store-read tripwire fires because thirdweb is now in 11 new RPC benches that are all warming up (dataConfidence="insufficient", rank=0 everywhere). Tripwire now requires at least one appearance with confident data before throwing.

Test plan

• alternatives/dydx, /alternatives/gains, /alternatives/hyperliquid, /alternatives/polymarket return 200
• /products/polymarket returns 200
• /products/thirdweb returns 200
• CI smoke test passes