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.BattleNode/Sessions/Participants/NoOpBotParticipant.cs

@@ -14,22 +14,25 @@ namespace SVSim.BattleNode.Sessions.Participants;
 /// </summary>
 public sealed class NoOpBotParticipant : IBattleParticipant
 {
+    /// <summary>Stub card-master id stamped on the bot's (never-read) MatchContext.</summary>
+    private const string BotCardMasterName = "card_master_node_10015";
+
     public long ViewerId => ServerBattleFrames.FakeOpponentViewerId;
     public MatchContext Context { get; } = new(
         SelfDeckCardIds: Array.Empty<long>(),
-        ClassId: "0", CharaId: "0", CardMasterName: "card_master_node_10015",
+        ClassId: "0", CharaId: "0", CardMasterName: BotCardMasterName,
         CountryCode: "", UserName: "Bot", SleeveId: "0",
         EmblemId: "0", DegreeId: "0", FieldId: 0, IsOfficial: 0,
         BattleType: 0);
 
+    // Required by IBattleParticipant, but a silent bot never raises it — suppress the
+    // "event is never used" warning rather than keeping a dead null-emitting method.
+#pragma warning disable CS0067
     public event Func<MsgEnvelope, CancellationToken, Task>? FrameEmitted;
+#pragma warning restore CS0067
 
     public Task PushAsync(MsgEnvelope envelope, bool noStock, CancellationToken ct) => Task.CompletedTask;
     public Task RunAsync(CancellationToken ct) => Task.CompletedTask;
     public Task TerminateAsync(BattleFinishReason reason) => Task.CompletedTask;
     public ValueTask DisposeAsync() => ValueTask.CompletedTask;
-
-    // Suppress unused-event warning — FrameEmitted is declared by the interface contract;
-    // intentionally never invoked.
-    private void Touch() => FrameEmitted?.Invoke(null!, default);
 }