fix(pm): data quality + geo bench refresh

[Flotapponnier]

Summary

• Myriad API retry: sort=volume_notional intermittently returns 500; falls back to volume_notional_24h automatically before giving up
• DeFiLlama volume for Polymarket: adds /summary/dexs/polymarket-international call in the DeFiLlama loop — this gives accurate vol24h/vol30d covering all trades (not just active markets). Gracefully falls back to gamma-api values if endpoint is unavailable.
• Myriad type fix: corrected from offchain to onchain / chain: abstract (Myriad Protocol runs on the Abstract L2)
• Remove PredictIt + Smarkets from hub: both showed all-null rows since no harness; removed from PM_VENUES until data is available
• ForecastEx in geo bench: replaces Manifold (play-money, no geo interest) in the geographic access probe — ForecastEx (CFTC-regulated by Interactive Brokers) is a US-regulated venue that may exhibit geo restrictions from non-US regions

Test plan

• Staging: /prediction-markets hub shows 4 venues (no PredictIt, no Smarkets, Myriad shows "On chain / abstract")
• VPS logs after rebuild: look for [defillama-vol][polymarket] vol24h= line — if DeFiLlama dexs endpoint resolves, vol24h should be materially higher than gamma-api's $3.5M
• VPS logs: [myriad] should not show 500 errors any more (retries to fallback sort)
• VPS geo logs: [geo][forecastex] probe lines appear