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/data/market/future_price.go

@@ -36,27 +36,50 @@ func (ms *MarketData) GetFuturePrice(symbol string) (float64, float64, int64, bo
 	return markPrice, fundingRate, p.NextFundingTime, true
 }
 
-func (ms *MarketData) GetAllFundRate() (map[string]float64, map[string]int64) {
+type PremiumIndex struct {
+	MarkPrice       float64
+	FundingRate     float64
+	NextFundingTime int64
+}
+
+func (ms *MarketData) GetAllPremiumIndex() (map[string]PremiumIndex, error) {
 	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 	defer cancel()
 
 	premiums, err := ms.futuresClient.NewPremiumIndexService().Do(ctx)
 	if err != nil {
 		log.Error().Err(err).Msg("Failed to fetch all futures premium index")
-		return make(map[string]float64), make(map[string]int64)
+		return nil, err
 	}
 
-	rates := make(map[string]float64, len(premiums))
-	times := make(map[string]int64, len(premiums))
-
+	result := make(map[string]PremiumIndex, len(premiums))
 	for _, p := range premiums {
-		rate, err := strconv.ParseFloat(p.LastFundingRate, 64)
+		markPrice, err := strconv.ParseFloat(p.MarkPrice, 64)
 		if err != nil {
 			continue
 		}
-		rates[p.Symbol] = rate
-		times[p.Symbol] = p.NextFundingTime
+		rate, _ := strconv.ParseFloat(p.LastFundingRate, 64)
+		result[p.Symbol] = PremiumIndex{
+			MarkPrice:       markPrice,
+			FundingRate:     rate,
+			NextFundingTime: p.NextFundingTime,
+		}
 	}
 
+	return result, nil
+}
+
+func (ms *MarketData) GetAllFundRate() (map[string]float64, map[string]int64) {
+	all, err := ms.GetAllPremiumIndex()
+	if err != nil {
+		return make(map[string]float64), make(map[string]int64)
+	}
+
+	rates := make(map[string]float64, len(all))
+	times := make(map[string]int64, len(all))
+	for sym, p := range all {
+		rates[sym] = p.FundingRate
+		times[sym] = p.NextFundingTime
+	}
 	return rates, times
 }