refactor: reuse position distance for attacks

src/Domain/CombatEngine.php

@@ -53,8 +53,7 @@ final class CombatEngine
             throw new CombatException('Target must be an active enemy unit.');
         }
 
-        $distance = abs($attacker->position->x - $target->position->x)
-            + abs($attacker->position->y - $target->position->y);
+        $distance = $attacker->position->distanceTo($target->position);
 
         if ($distance !== 1) {
             throw new CombatException('Target is outside attack range.');