feat(battle-node): IMatchingBridge + MatchingBridge mint battle id + node url

SVSim.BattleNode/Bridge/IMatchingBridge.cs

@@ -0,0 +1,12 @@
+namespace SVSim.BattleNode.Bridge;
+
+public interface IMatchingBridge
+{
+    /// <summary>
+    /// Mint a battle id, register a pending session for the given viewer, and return the
+    /// URL the client should open a socket to.
+    /// </summary>
+    PendingMatch RegisterPendingBattle(long viewerId);
+}
+
+public sealed record PendingMatch(string BattleId, string NodeServerUrl);