test(battle-engine M13): HeadlessNetworkBattleMgr constructs headless (construction probe)

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

SVSim.BattleEngine.Tests/NetworkMgrConstructionProbeTests.cs

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+using NUnit.Framework;
+using SVSim.BattleEngine.Rng;
+using Wizard.BattleMgr;
+
+namespace SVSim.BattleEngine.Tests
+{
+    // M13 step 1 (the M2 ConstructionProbe pattern): can a NetworkBattleManagerBase-derived mgr be
+    // built headless at all? NetworkBattleManagerSetup constructs NetworkTouchControl(this,
+    // _battleCamera, _backGround) + RegisterActionManager + OperateReceive — the largest new shim
+    // surface since M5's prefab path. Isolate "ctor runs" before any play is driven.
+    [TestFixture]
+    public class NetworkMgrConstructionProbeTests
+    {
+        [Test]
+        public void HeadlessNetworkBattleMgr_constructs_headless()
+        {
+            HeadlessEngineEnv.EnsureInitialized();
+            Assert.DoesNotThrow(() =>
+            {
+                var mgr = new HeadlessNetworkBattleMgr(new HeadlessContentsCreator());
+                Assert.That(mgr, Is.Not.Null);
+            });
+        }
+    }
+}