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

SVSim.BattleNode/Bridge/BattleNodeOptions.cs

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+namespace SVSim.BattleNode.Bridge;
+
+/// <summary>
+/// DI-injected options for the battle node. The web host populates these — typically
+/// nodeServerUrl is "ws://localhost:5148" matching ASPNETCORE_URLS.
+/// </summary>
+public sealed class BattleNodeOptions
+{
+    public string NodeServerUrl { get; set; } = "ws://localhost:5148";
+}

SVSim.BattleNode/Bridge/IMatchingBridge.cs

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+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);

SVSim.BattleNode/Bridge/MatchingBridge.cs

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+using SVSim.BattleNode.Sessions;
+
+namespace SVSim.BattleNode.Bridge;
+
+public sealed class MatchingBridge : IMatchingBridge
+{
+    private readonly IBattleSessionStore _store;
+    private readonly BattleNodeOptions _options;
+
+    public MatchingBridge(IBattleSessionStore store, BattleNodeOptions options)
+    {
+        _store = store;
+        _options = options;
+    }
+
+    public PendingMatch RegisterPendingBattle(long viewerId)
+    {
+        // 12-digit decimal battle id mirrors the captures (e.g. "975695075012").
+        var battleId = (Math.Abs(Guid.NewGuid().GetHashCode()) % 1_000_000_000_000L).ToString("D12");
+        _store.RegisterPending(new PendingBattle(battleId, viewerId));
+        return new PendingMatch(battleId, _options.NodeServerUrl);
+    }
+}

SVSim.UnitTests/BattleNode/Bridge/MatchingBridgeTests.cs

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+using NUnit.Framework;
+using SVSim.BattleNode.Bridge;
+using SVSim.BattleNode.Sessions;
+
+namespace SVSim.UnitTests.BattleNode.Bridge;
+
+[TestFixture]
+public class MatchingBridgeTests
+{
+    [Test]
+    public void RegisterPendingBattle_RegistersInStoreAndReturnsNodeUrl()
+    {
+        var store = new InMemoryBattleSessionStore();
+        var bridge = new MatchingBridge(store, new BattleNodeOptions { NodeServerUrl = "ws://localhost:5148" });
+
+        var match = bridge.RegisterPendingBattle(viewerId: 906243102);
+
+        Assert.That(match.NodeServerUrl, Is.EqualTo("ws://localhost:5148"));
+        Assert.That(match.BattleId, Is.Not.Empty);
+        var pending = store.TryGetPending(match.BattleId);
+        Assert.That(pending, Is.Not.Null);
+        Assert.That(pending!.ViewerId, Is.EqualTo(906243102));
+    }
+
+    [Test]
+    public void RegisterPendingBattle_MintsUniqueBattleIds()
+    {
+        var bridge = new MatchingBridge(new InMemoryBattleSessionStore(), new BattleNodeOptions());
+
+        var a = bridge.RegisterPendingBattle(1);
+        var b = bridge.RegisterPendingBattle(2);
+
+        Assert.That(a.BattleId, Is.Not.EqualTo(b.BattleId));
+    }
+}