Rewrite price lookup from WebSocket to REST API

Replace unreliable WebSocket connections with on-demand REST API calls
for spot and futures prices. Add cached trading pair list (refreshed
hourly) for symbol validation, and /refresh command for manual updates.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/data/market/trading_pairs.go

@@ -0,0 +1,73 @@
+package market
+
+import (
+	"context"
+	"time"
+
+	"github.com/rs/zerolog/log"
+)
+
+func (ms *MarketData) refreshTradingPairCache() {
+	ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
+	defer cancel()
+
+	spotInfo, err := ms.spotClient.NewExchangeInfoService().Do(ctx)
+	if err != nil {
+		log.Error().Err(err).Msg("Failed to fetch spot exchange info")
+		return
+	}
+
+	futuresInfo, err := ms.futuresClient.NewExchangeInfoService().Do(ctx)
+	if err != nil {
+		log.Error().Err(err).Msg("Failed to fetch futures exchange info")
+		return
+	}
+
+	ms.pairCacheMutex.Lock()
+	defer ms.pairCacheMutex.Unlock()
+
+	ms.spotPairs = make(map[string]bool, len(spotInfo.Symbols))
+	for _, s := range spotInfo.Symbols {
+		if s.Status == "TRADING" {
+			ms.spotPairs[s.Symbol] = true
+		}
+	}
+
+	ms.futuresPairs = make(map[string]bool, len(futuresInfo.Symbols))
+	for _, s := range futuresInfo.Symbols {
+		if s.Status == "TRADING" {
+			ms.futuresPairs[s.Symbol] = true
+		}
+	}
+
+	ms.lastPairCacheUpdate = time.Now()
+	log.Info().
+		Int("spot", len(ms.spotPairs)).
+		Int("futures", len(ms.futuresPairs)).
+		Msg("Trading pair cache refreshed")
+}
+
+func (ms *MarketData) pairCacheRefreshLoop() {
+	ms.refreshTradingPairCache()
+	ticker := time.NewTicker(time.Hour)
+	defer ticker.Stop()
+	for range ticker.C {
+		ms.refreshTradingPairCache()
+	}
+}
+
+func (ms *MarketData) IsSpotPair(symbol string) bool {
+	ms.pairCacheMutex.RLock()
+	defer ms.pairCacheMutex.RUnlock()
+	return ms.spotPairs[symbol]
+}
+
+func (ms *MarketData) IsFuturesPair(symbol string) bool {
+	ms.pairCacheMutex.RLock()
+	defer ms.pairCacheMutex.RUnlock()
+	return ms.futuresPairs[symbol]
+}
+
+func (ms *MarketData) RefreshTradingPairCache() {
+	ms.refreshTradingPairCache()
+}