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/Protocol/Bodies/PlayActionsBroadcastBody.cs

@@ -32,7 +32,8 @@ public sealed record KeyActionEntry(
 /// Only emitted for the open:1 pass-through case (open:0 strips the whole <c>selectCard</c>).</summary>
 public sealed record SelectCardEntry(
     [property: JsonPropertyName("cardId")] IReadOnlyList<long> CardId,
-    [property: JsonPropertyName("open")] int Open);
+    [property: JsonPropertyName("open")]
+    [property: JsonConverter(typeof(JsonNumberEnumConverter<ChoiceVisibility>))] ChoiceVisibility Open);
 
 /// <summary>One revealed card in a <c>knownList</c>. Vanilla slice fills cardId from the sender's
 /// deck map and leaves spellboost 0 / attachTarget "" (cost/clan/tribe deferred to the card-master
@@ -48,7 +49,8 @@ public sealed record KnownCardEntry(
 /// verbatim — no perspective flip (bullet-3 audit F2).</summary>
 public sealed record OppoTargetEntry(
     [property: JsonPropertyName("targetIdx")] int TargetIdx,
-    [property: JsonPropertyName("isSelf")] int IsSelf);
+    [property: JsonPropertyName("isSelf")]
+    [property: JsonConverter(typeof(JsonNumberEnumConverter<CardOwner>))] CardOwner IsSelf);
 
 /// <summary>One entry in a relayed <c>uList</c> (the unapproved-movement list) — a skill-driven
 /// card movement (fetch / search / summon-from-deck / discard-reveal) the node forwards VERBATIM
@@ -60,12 +62,14 @@ public sealed record UnapprovedCardEntry(
     [property: JsonPropertyName("idxList")] IReadOnlyList<int> IdxList,
     [property: JsonPropertyName("from")] int From,
     [property: JsonPropertyName("to")] int To,
-    [property: JsonPropertyName("isSelf")] int IsSelf,
+    [property: JsonPropertyName("isSelf")]
+    [property: JsonConverter(typeof(JsonNumberEnumConverter<CardOwner>))] CardOwner IsSelf,
     [property: JsonPropertyName("skill")] string Skill,
     [property: JsonPropertyName("cardId")] long? CardId = null,
     [property: JsonPropertyName("clan")] int? Clan = null,
     [property: JsonPropertyName("cost")] int? Cost = null,
     [property: JsonPropertyName("skillKeyCardIdx")] IReadOnlyList<int>? SkillKeyCardIdx = null,
     [property: JsonPropertyName("randomTargetIdx")] IReadOnlyList<int>? RandomTargetIdx = null,
-    [property: JsonPropertyName("isInvoke")] int? IsInvoke = null,
+    [property: JsonPropertyName("isInvoke")]
+    [property: JsonConverter(typeof(NumericBoolJsonConverter))] bool? IsInvoke = null,
     [property: JsonPropertyName("attachTarget")] string? AttachTarget = null);