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.BattleNode/Reliability/Gungnir.cs

@@ -3,8 +3,9 @@ namespace SVSim.BattleNode.Reliability;
 /// <summary>
 /// Body builders for the alive channel ("Gungnir" is the client's codename for the
 /// keepalive/connection-status channel — see <see cref="Protocol.Bodies.AlivePushBody"/>).
-/// The timer/loop that drives <see cref="EmitInterval"/> emits lives on
-/// BattleSession; this class is just the pure body-shape factory.
+/// The timer/loop that would drive the emit cadence
+/// (<see cref="Bridge.BattleNodeOptions.AliveEmitInterval"/>) is to live on BattleSession;
+/// this class is just the pure body-shape factory.
 /// v1 always reports scs/ocs=ONLINE — real disconnect detection is deferred. The push
 /// body itself is constructed inline in BattleSession.HandleAliveEventAsync using
 /// AlivePushBody; only the emit body (sent by us TO the client on the alive channel,
@@ -12,8 +13,6 @@ namespace SVSim.BattleNode.Reliability;
 /// </summary>
 public static class Gungnir
 {
-    public static readonly TimeSpan EmitInterval = TimeSpan.FromSeconds(5);
-
     public static Dictionary<string, object?> BuildAliveEmitBody(InboundTracker tracker) => new()
     {
         ["currentSeq"] = tracker.HighWaterMark,