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/MatchContext.cs

@@ -12,12 +12,25 @@ public sealed record MatchContext(
     IReadOnlyList<long> SelfDeckCardIds,
 
     // Player class + leader (BattleStartSelfInfo)
-    string ClassId,         // "1".."8"
-    string CharaId,         // "1".."8" — equals ClassId when no leader skin chosen
+
+    /// <summary>The player's class. Rendered onto the wire <c>classId</c> as <c>"1".."8"</c> via
+    /// <see cref="CardClassWire.ToWireValue"/>; a closed set, so it's typed, not stringly.</summary>
+    CardClass ClassId,
+
+    /// <summary>Leader/skin id on the wire <c>charaId</c>. FREE-FORM, not a class enum: it's the
+    /// equipped leader-skin id (e.g. <c>"5000123"</c>) when one is chosen, else the class ordinal
+    /// (<c>"1".."8"</c>). Passed through verbatim — the node never interprets it.</summary>
+    string CharaId,
+
     string CardMasterName,  // current card-master, e.g. "card_master_node_10015"
 
     // Player cosmetics (MatchedSelfInfo)
-    string CountryCode,     // "KOR", "JPN", ...
+
+    /// <summary>Account region code, wire <c>country_code</c>. OPEN-ENDED account data (any value,
+    /// possibly empty); the node never branches on it. <see cref="CountryCodes"/> names the values
+    /// seen in captures.</summary>
+    string CountryCode,
+
     string UserName,
     string SleeveId,
     string EmblemId,