fix: preserve futures token identity in canonical cache

Keep futureToken2Symbol keyed by raw futures token and use explicit spot-to-future alias mapping during resolver fallback lookups.

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

internal/data/market/trading_pairs.go

@@ -69,7 +69,7 @@ func (ms *MarketData) refreshFuturePairCache() error {
 		if token == "" {
 			continue
 		}
-		token = normalizeFutureToken(token)
+		token = futureCacheTokenKey(token)
 		futureTokenCandidates[token] = append(futureTokenCandidates[token], s.Symbol)
 	}
 
@@ -168,12 +168,8 @@ func selectCanonicalSymbolByQuotePriority(token string, candidates []string) str
 	return normalized[0]
 }
 
-func normalizeFutureToken(token string) string {
-	token = strings.ToUpper(token)
-	if mapped, ok := binance.FutureToken2SpotTokenMap[token]; ok {
-		return strings.ToUpper(mapped)
-	}
-	return token
+func futureCacheTokenKey(token string) string {
+	return strings.ToUpper(token)
 }
 
 func (ms *MarketData) IsSpotPair(symbol string) bool {