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/tele/commands/market.go

@@ -1,7 +1,11 @@
 package commands
 
 import (
+	"os"
+	"strconv"
+
 	"gopkg.in/telebot.v3"
+	"me.thuanle/bbot/internal/configs/key"
 	"me.thuanle/bbot/internal/data"
 	"me.thuanle/bbot/internal/services/controllers"
 	"me.thuanle/bbot/internal/services/tele/chat"
@@ -19,6 +23,10 @@ func OnGetTopFundingFee(context telebot.Context) error {
 }
 
 func OnRefreshPairCache(context telebot.Context) error {
+	adminID, _ := strconv.ParseInt(os.Getenv(key.AdminChatID), 10, 64)
+	if adminID != 0 && context.Sender().ID != adminID {
+		return nil
+	}
 	data.Market.RefreshTradingPairCache()
 	return chat.ReplyMessage(context, "Trading pair cache refreshed")
 }