refactor(battlenode): type MatchContext.ClassId as CardClass enum (§C)

Behavior-preserving; full solution builds, 1013 tests green.

ClassId is the one genuinely-closed set of the three flagged stringly fields, so it
becomes a CardClass enum (1..8). Wire stays "1".."8": producer casts
(CardClass)run.ClassId, ServerBattleFrames renders via CardClassWire.ToWireValue().
RankBattleController's AI-start path drops a fragile int.TryParse(...)?:-1 for (int)cast.

CharaId (free-form leader/skin id, e.g. "5000123") and CountryCode (open-ended account
data) stay string with proper XML docs; CountryCodes.Korea/Japan name the captured values.

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

SVSim.BattleNode/Bridge/CardClass.cs

@@ -0,0 +1,29 @@
+namespace SVSim.BattleNode.Bridge;
+
+/// <summary>
+/// A Shadowverse class (craft). The wire carries it as the stringified ordinal (<c>"1".."8"</c> on
+/// the <c>classId</c> field); this enum replaces that stringly-typed value on
+/// <see cref="MatchContext.ClassId"/> so the legal set lives in the type, not a trailing comment.
+/// <see cref="None"/> covers an unset / placeholder context. Use <see cref="CardClassWire.ToWireValue"/>
+/// to render the wire string.
+/// </summary>
+public enum CardClass
+{
+    None = 0,
+    Forestcraft = 1,
+    Swordcraft = 2,
+    Runecraft = 3,
+    Dragoncraft = 4,
+    Shadowcraft = 5,
+    Bloodcraft = 6,
+    Havencraft = 7,
+    Portalcraft = 8,
+}
+
+/// <summary>Wire rendering for <see cref="CardClass"/>.</summary>
+public static class CardClassWire
+{
+    /// <summary>The <c>classId</c> wire value — the class ordinal as a string (<c>"1".."8"</c>,
+    /// <c>"0"</c> for <see cref="CardClass.None"/>), matching what the client sends/expects.</summary>
+    public static string ToWireValue(this CardClass cardClass) => ((int)cardClass).ToString();
+}