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/Dispatch/Handlers/LoadedHandler.cs

@@ -17,8 +17,8 @@ internal sealed class LoadedHandler : IFrameHandler
         // case 6: general — BattleStart (per-perspective) + Deal to the sender.
         if (ctx.SenderPhase == BattleSessionPhase.AwaitingLoaded)
         {
-            // A goes first deterministically (turnState 0); B goes second (turnState 1).
-            var turnState = ReferenceEquals(ctx.From, ctx.A) ? 0 : 1;
+            // A goes first deterministically; B goes second.
+            var turnState = ReferenceEquals(ctx.From, ctx.A) ? TurnState.First : TurnState.Second;
             var r = new List<DispatchRoute>
             {
                 new(ctx.From, ServerBattleFrames.BuildBattleStart(