feat(battle-node): add MatchContext record for per-mode player snapshot

Public contract between HTTP-side do_matching controllers (assemble) and
SVSim.BattleNode (consume). First piece of the real-drafted-deck wiring;
nothing references it yet.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.BattleNode/Bridge/MatchContext.cs

@@ -0,0 +1,29 @@
+namespace SVSim.BattleNode.Bridge;
+
+/// <summary>
+/// Per-battle player snapshot captured at do_matching time and replayed into the scripted
+/// lifecycle on WS connect. SVSim.BattleNode does not know how to build this — the HTTP-side
+/// per-mode controller is the source. Snapshot semantics: cosmetic changes between matching
+/// and WS connect have no effect on the in-battle render.
+/// </summary>
+public sealed record MatchContext(
+    // Player's drafted deck — exactly 30 entries, idx 1..30 paired with the chosen cardIds
+    // in the order this list provides them. Producer is responsible for the count.
+    IReadOnlyList<long> SelfDeckCardIds,
+
+    // Player class + leader (BattleStartSelfInfo)
+    string ClassId,         // "1".."8"
+    string CharaId,         // "1".."8" — equals ClassId when no leader skin chosen
+    string CardMasterName,  // current card-master, e.g. "card_master_node_10015"
+
+    // Player cosmetics (MatchedSelfInfo)
+    string CountryCode,     // "KOR", "JPN", ...
+    string UserName,
+    string SleeveId,
+    string EmblemId,
+    string DegreeId,
+    int    FieldId,
+    int    IsOfficial,      // 0 or 1
+
+    // Battle-mode hint, currently TK2 == 11. Future modes populate their own value.
+    int    BattleType);