refactor(battle-node): de-magic wire flags and scattered constants

Quality pass from the 2026-06-04 BattleNode review (audit in the outer
repo). All changes are behavior-preserving — identical wire bytes,
verified by the full 1008-test suite staying green.

- Name scattered magic numbers: crypto key/IV lengths, outbound-sequencer
  base, WS receive buffer / EIO ping / SID length, polite-close timeout,
  upgrade-credential keys, battle-id digit math, deterministic-turn spin.
- resultCode = 1 -> (int)ReceiveNodeResultCode.Success across body records.
- Pong "3" -> EngineIoPacketType.Pong; remove dead NoOpBotParticipant.Touch
  (replace with #pragma warning disable CS0067).
- Wire-flag enums, serialized as numbers via JsonNumberEnumConverter:
  turnState -> TurnState{First,Second}, isSelf -> CardOwner{Opponent,Self},
  open -> ChoiceVisibility{Hidden,Open}.
- isOfficial / isInvoke -> bool / bool? via new NumericBoolJsonConverter
  (reads/writes 0/1; TDD'd). Scoped to the BattleNode wire boundary only;
  MatchContext and the HTTP/AI-start path stay int (AI-start uses -1 as a
  sentinel, so it is not boolean).

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

SVSim.UnitTests/BattleNode/Lifecycle/ServerBattleFramesTests.cs

@@ -65,15 +65,15 @@ public class ServerBattleFramesTests
         Assert.That(body.SelfInfo.EmblemId, Is.EqualTo("888"));
         Assert.That(body.SelfInfo.DegreeId, Is.EqualTo("777"));
         Assert.That(body.SelfInfo.FieldId, Is.EqualTo(42));
-        Assert.That(body.SelfInfo.IsOfficial, Is.EqualTo(1));
+        Assert.That(body.SelfInfo.IsOfficial, Is.True);
     }
 
     [Test]
     public void BuildBattleStart_HasTurnStateZero_AndUsesContextBattleType()
     {
-        var env = ServerBattleFrames.BuildBattleStart(FixtureCtx(), FakeOpponentCtx(), selfViewerId: 1, turnState: 0);
+        var env = ServerBattleFrames.BuildBattleStart(FixtureCtx(), FakeOpponentCtx(), selfViewerId: 1, turnState: TurnState.First);
         var body = (BattleStartBody)env.Body;
-        Assert.That(body.TurnState, Is.EqualTo(0));
+        Assert.That(body.TurnState, Is.EqualTo(TurnState.First));
         Assert.That(body.BattleType, Is.EqualTo(11));
     }
 
@@ -87,7 +87,7 @@ public class ServerBattleFramesTests
             BattleType = 42,
         };
 
-        var env = ServerBattleFrames.BuildBattleStart(ctx, FakeOpponentCtx(), selfViewerId: 1, turnState: 0);
+        var env = ServerBattleFrames.BuildBattleStart(ctx, FakeOpponentCtx(), selfViewerId: 1, turnState: TurnState.First);
         var body = (BattleStartBody)env.Body;
 
         Assert.That(body.SelfInfo.ClassId, Is.EqualTo("7"));

SVSim.UnitTests/BattleNode/Lifecycle/TypedBodyWireShapeTests.cs

@@ -87,7 +87,7 @@ public class TypedBodyWireShapeTests
     [Test]
     public void BuildBattleStart_SerializesAllWireKeysAndPreservesBattlePointAsymmetry()
     {
-        var env = ServerBattleFrames.BuildBattleStart(FixtureCtx(), FakeOpponentCtx(), selfViewerId: 906243102, turnState: 0);
+        var env = ServerBattleFrames.BuildBattleStart(FixtureCtx(), FakeOpponentCtx(), selfViewerId: 906243102, turnState: TurnState.First);
 
         var json = MsgEnvelope.ToJson(env);
         var node = JsonNode.Parse(json)!.AsObject();