feat: fetch alpha price by symbol ticker

Keep alpha token existence from list cache and fetch live alpha price via symbol ticker endpoint for richer token response accuracy.

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

internal/data/imarket.go

@@ -13,6 +13,7 @@ type IMarket interface {
 	// Alpha token methods
 	IsAlphaToken(symbol string) bool
 	GetAlphaToken(symbol string) (market.AlphaTokenInfo, bool)
+	GetAlphaPrice(symbol string) (float64, bool)
 
 	// Trading pair methods
 	IsSpotPair(symbol string) bool