fix: Declare stop_price and use reassignment operator in strategy

pinescripts/Three_ATR_EMA.pine

@@ -18,6 +18,7 @@ bullish_entry = (close < ema) and
                (close > close[1])
 
 // Trailing Stop Logic
+var float stop_price = na
 var float trail_price = na
 var bool trail_active = false
 
@@ -35,8 +36,8 @@ if strategy.position_size > 0
     if trail_active
         trail_price := math.max(high, nz(trail_price, high))
     
-    // Calculate stop price
-    stop_price = trail_active ? trail_price * (1 - trail_percent/100) : na
+    // Calculate stop price (now using declared variable)
+    stop_price := trail_active ? trail_price * (1 - trail_percent/100) : na
     
     // Submit exit order
     if trail_active