decouple display from trading: snapMu + RefreshSnapshot/ReadSnapshot

- Add snapMu RWMutex + positionsSnapshot to Trader
- RefreshSnapshot() called from main loop after Tick() — acquires
  t.mu briefly, stores deep copy under snapMu
- ReadSnapshot() returns snapshot copy under snapMu.RLock — never
  touches t.mu, zero contention with trading path
- Dashboard + handleStatus + hourly summary + status log all
  use ReadSnapshot() instead of GetPositionsCopy()
- Trading path (Tick/TryEntry/executeEntry/checkExit/checkScaleIn)
  never blocked by display reads
- Snapshot is at most 1 tick behind live state — acceptable delay

main.go

@@ -147,8 +147,8 @@ func main() {
 			}
 			log.Printf("[Status] %d prices / %d coins connected", count, len(snap))
 
-			// Show open positions
-			if positions := trader.GetOpenPositions(); len(positions) > 0 {
+			// Show open positions (read from decoupled snapshot)
+			if positions := trader.ReadSnapshot(); len(positions) > 0 {
 				for _, pos := range positions {
 					log.Printf("  [Position] %s %s open %d scales $%.0f since %s",
 						pos.Coin, pos.Direction, pos.ScaleLevels, pos.AmountUSD,
@@ -162,6 +162,7 @@ func main() {
 
 			// Tick the trader (monitor open positions for exit)
 			trader.Tick(store, notifier)
+			trader.RefreshSnapshot() // decoupled snapshot for display
 			t1 := time.Now()
 
 			// Scan for arbitrage entries using maker fees (limit orders)
@@ -190,7 +191,7 @@ func main() {
 			// Hourly trade summary — use hour-based tracking (wider window than second-granularity)
 			hour := now.Hour()
 			if hour != lastHour && now.Minute() < 1 {
-				positions := trader.GetPositionsCopy()
+				positions := trader.ReadSnapshot()
 				notifier.SendTradeSummary(positions, now.Format("2006-01-02 15:04"))
 				lastHour = hour
 			}