fix: remove HL-delisted coins from scanner (BNT/CATI/CYBER/ILV/LISTA/OGN/STG) + PIXEL

Root cause: HL WS uses allMids (all coins), BG WS subscribes per-coin.
Delisted coins had stale HL prices showing huge fake spreads (~200%).
Monitor tried entry → BG buy succeeds, HL sell fails (Trading is halted)
→ orphan position on BG accumulated across restarts.

Fix:
- Set HL="" for BNT, CATI, CYBER, ILV, LISTA, OGN, STG, PIXEL
- Add guard in ScanBGHL to skip coins where BG or HL is empty
- Same guard in SpreadWindowTracker.Tick

test_bg.go

@@ -0,0 +1,33 @@
+//go:build ignore
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	"exchange-monitor/exchange"
+)
+
+func main() {
+	b, _ := os.ReadFile(".env")
+	m := map[string]string{}
+	for _, l := range strings.Split(string(b), "\n") {
+		l = strings.TrimSpace(l)
+		if l == "" || l[0] == '#' { continue }
+		if i := strings.Index(l, "="); i > 0 {
+			m[strings.TrimSpace(l[:i])] = strings.TrimSpace(l[i+1:])
+		}
+	}
+
+	bg := exchange.NewBitgetTrade(m["BITGET_API_KEY"], m["BITGET_API_SECRET"], m["BITGET_PASSPHRASE"])
+	bal, err := bg.GetBalance()
+	if err != nil {
+		fmt.Printf("BG balance error: %v\n", err)
+	} else {
+		fmt.Printf("BG balance: $%.2f\n", bal)
+	}
+	
+	fmt.Println("\nKey prefix:", string(m["BITGET_API_KEY"][:5]))
+}