refactor(battlenode): low-churn §B/§D/§E/§F quality cleanups

Behavior-preserving; 231 BattleNode tests green.

- §D: MsgEnvelope.Try -> RetryAttempt (drops keyword-escape; wire key stays "try");
  SocketIoFrame.AckResponse arg -> pubSeqEcho.
- §B: Gungnir.EmitInterval -> BattleNodeOptions.AliveEmitInterval (unused literal
  moved to its config home); deck-idx 4L -> InitialHand.Length + 1.
- §E: shared Wire.WireJsonOptions.CamelCase replaces the duplicated camelCase
  JsonSerializerOptions in EngineIoHandshake and MsgEnvelope.
- §F: do-NOT-consistency-fix polarity notes on TurnEndFinalHandler (From wins)
  and RetireKillHandler (From loses).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

SVSim.UnitTests/BattleNode/Wire/SocketIoFrameTests.cs

@@ -72,7 +72,7 @@ public class SocketIoFrameTests
     [Test]
     public void Encode_AckResponse_IsTypeIdAndArrayOfArgs()
     {
-        var frame = SocketIoFrame.AckResponse(ackId: 7, arg: 123);
+        var frame = SocketIoFrame.AckResponse(ackId: 7, pubSeqEcho: 123);
         var (text, bins) = frame.Encode();
 
         Assert.That(text, Is.EqualTo("37[123]"));