fix(kalshi-res): exclude Exotics, add event category cache

[Flotapponnier]

Problem

The previous Kalshi poller had two critical issues making the comparison unfair:

1. All categories mapped to "other" — Kalshi /markets API returns no category field. Every market was hitting the default: "other" branch.

2. Exotics (auto-generated parlays) dominated data — The 1000 most recently settled Kalshi markets were 100% KXMV* multivariate parlays that Kalshi auto-settles algorithmically in 0–200 seconds. These are not prediction market questions and have no equivalent on Polymarket. Their inclusion was pulling Kalshi's p50 to ~3 minutes, which would have read as "Kalshi resolves 20x faster than Polymarket" — technically true but comparing algorithmic settlement to UMA's 2h challenge window.

Fix

• pollFinalized now fetches event category lazily via /events/{event_ticker} (in-memory cache, one HTTP call per unique event, ~50–150 events per poll cycle)
• Markets with Kalshi category Exotics are excluded (and marked recorded to skip on next poll)
• Category mapping: Sports→sports, Politics/Elections→politics, Crypto/Financials→crypto, rest→other
• Bench YAML methodology note added explaining anchor asymmetry (Polymarket 2h protocol floor vs Kalshi no floor)

VPS

Deploy separately after merge (rebuild needed).