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

trader.go

@@ -89,6 +89,26 @@ func (t *Trader) GetPositionsCopy() []ArbPosition {
 	return r
 }
 
+// RefreshSnapshot takes a trading-lock snapshot of open positions for display use.
+// Call this after each Tick() from the main loop — never during a trading operation.
+// The display reads from this snapshot without blocking trading.
+func (t *Trader) RefreshSnapshot() {
+	copy := t.GetPositionsCopy() // acquires t.mu briefly (not held during Tick call)
+	t.snapMu.Lock()
+	t.positionsSnapshot = copy
+	t.snapMu.Unlock()
+}
+
+// ReadSnapshot returns a copy of the last display snapshot — never locks t.mu.
+// Safe to call from any goroutine without impacting trading latency.
+func (t *Trader) ReadSnapshot() []ArbPosition {
+	t.snapMu.RLock()
+	defer t.snapMu.RUnlock()
+	r := make([]ArbPosition, len(t.positionsSnapshot))
+	copy(r, t.positionsSnapshot)
+	return r
+}
+
 // Trader handles scalable arbitrage between Bitget and HyperLiquid.
 type Trader struct {
 	cfg         *Config
@@ -102,6 +122,10 @@ type Trader struct {
 	closedTrades  []TradeRecord // history of closed trades
 
 	OnTradeEvent func(event string, data interface{}) // P3-4: real-time SSE push
+
+	// Decoupled snapshot for display — snapMu never contended by trading path
+	snapMu            sync.RWMutex
+	positionsSnapshot []ArbPosition
 }
 
 // TradeRecord stores a finalized trade for stats tracking.