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/Integration/BattleNodeFlowTests.cs

@@ -119,7 +119,7 @@ public class BattleNodeFlowTests
 
     private static MsgEnvelope MakeEnvelopeWith(long vid, NetworkBattleUri uri, long pubSeq,
         Dictionary<string, object?>? body = null) =>
-        new(uri, ViewerId: vid, Uuid: "udid-test", Bid: null, Try: 0,
+        new(uri, ViewerId: vid, Uuid: "udid-test", Bid: null, RetryAttempt: 0,
             Cat: uri == NetworkBattleUri.InitNetwork ? EmitCategory.General
                  : uri == NetworkBattleUri.InitBattle ? EmitCategory.Matching
                  : EmitCategory.Battle,