fix(battle-node): assert Bid is in envelope (not Body) on BuildMatched

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SVSim.UnitTests/BattleNode/Lifecycle/ScriptedLifecycleTests.cs

@@ -17,6 +17,10 @@ public class ScriptedLifecycleTests
         Assert.That(selfInfo["oppoId"], Is.EqualTo(847666884L));
         var oppoInfo = (Dictionary<string, object?>)env.Body["oppoInfo"]!;
         Assert.That(oppoInfo["oppoId"], Is.EqualTo(906243102L));
+
+        // Bid travels in the envelope, not the Body — protect against the Task 5 reserved-keys regression.
+        Assert.That(env.Bid, Is.EqualTo("b"));
+        Assert.That(env.Body.ContainsKey("bid"), Is.False);
     }
 
     [Test]