fix: smoke gate 22 failures (308s, ISR 500s, noindex)

[Flotapponnier]

Summary

• sitemap-builder: exclude perp venue slugs that 308 to /perp/[slug] from products section (removes 13 x 308 failures)
• sitemap-builder: skip benches in "awaiting" state (editorial=live but no Prom data → noindex) from sitemap
• alternatives/[slug]: remove loadBenchFromBlob("perp-fees-at-size") call — cache:"no-store" fetch inside ISR page triggers Next.js "Page changed from static to dynamic" crash (removes 4 x 500 failures)
• prod-deploy: warm products/polymarket + alternatives perp pages before smoke so degraded-read tripwire clears