fix: data race, scale-in PnL, nonce mutex, dead code, hourly check

- 🔴 Data race: Add GetPositionsCopy() returning deep copies (no shared
  ArbPosition pointers). Use it in dashboard broadcastLoop + handleStatus.
- 🟡 Scale-in PnL: Track LongEntryPrices/ShortEntryPrices on ArbPosition,
  compute weighted average (harmonic mean) at exit for accurate PnL.
- 🟢 CalcNetProfit: Delete dead code from exchange/helpers.go.
- 🟢 HL nonce: Add sync.Mutex around lastNonce++ (thread safety).
- 🟢 Hourly check: Change from 5-second window to minute window.
- 🟢 ExitPrice: Test mode closeLeg already handled by checkExit.

exchange/helpers.go

@@ -1,42 +1,5 @@
 package exchange
 
-import "github.com/gorilla/websocket"
-
-// These are needed for compilation of the exchange package.
-// PriceConnector is defined in connector.go.
-var _ = websocket.ErrCloseSent // keep gorilla/websocket import
-
-// CalcNetProfit calculates net profit % for a complete round trip (entry + exit) between two exchanges.
-// buyPrice: price on the buy exchange
-// sellPrice: price on the sell exchange
-// buyFee: fee rate on buy exchange (e.g. 0.03 for 0.03%)
-// sellFee: fee rate on sell exchange
-// buyFee2: buy fee on the other exchange
-// sellFee2: sell fee on the other exchange
-// Returns net profit in percentage.
-func CalcNetProfit(price1, price2, fee1Buy, fee1Sell, fee2Buy, fee2Sell float64) float64 {
-	// price1 = Bitget, price2 = HyperLiquid
-	// Try: buy cheap (min), sell expensive (max)
-	buyPrice := price1
-	sellPrice := price2
-	buyFee := fee1Buy
-	sellFee := fee2Sell
-
-	if price2 < price1 {
-		buyPrice = price2
-		sellPrice = price1
-		buyFee = fee2Buy
-		sellFee = fee1Sell
-	}
-
-	// Entry: buy at buyPrice (pay buyFee), sell short at sellPrice (pay sellFee)
-	if buyPrice <= 0 || sellPrice <= 0 {
-		return 0
-	}
-	cost := buyPrice * (1 + buyFee/100)
-	revenue := sellPrice * (1 - sellFee/100)
-
-	// Exit: sell long (pay sellFee), buy back short (pay buyFee)
-	// Total fees = 2 * (buyFee + sellFee), first round already in formula above
-	return (revenue/cost-1)*100 - (buyFee + sellFee)
-}
+// Package-level helpers for the exchange package.
+// connector.go imports gorilla/websocket, so this file needs no imports
+// for that dependency. CalcNetProfit was removed (see netProfit in scanner.go).