Address PR #15 review: batch API calls and admin-guard /refresh

1. Add GetAllPremiumIndex() to fetch all futures data in one call,
   used by GetTopPrices instead of per-symbol sequential calls.
2. Add ADMIN_CHAT_ID env check to /refresh command to restrict
   access to authorized users only.

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

internal/services/controllers/market.go

@@ -13,15 +13,19 @@ func GetTopPrices() ([]string, []float64, []float64) {
 	topPrice := make([]float64, n)
 	topRate := make([]float64, n)
 
+	all, err := data.Market.GetAllPremiumIndex()
+	if err != nil {
+		return topSym, topPrice, topRate
+	}
+
 	for i, sym := range strategy.TopPriceSymbols {
-		price, rate, _, ok := data.Market.GetFuturePrice(sym)
+		p, ok := all[sym]
 		if !ok {
 			continue
 		}
 		topSym[i] = sym
-		topPrice[i] = price
-		topRate[i] = rate
-
+		topPrice[i] = p.MarkPrice
+		topRate[i] = p.FundingRate
 	}
 	return topSym, topPrice, topRate
 }