refactor(app): compose content effects and audio startup

Move Phase-2 startup behind typed composition/publication boundaries, replace the GameWindow-capturing PhysicsScript gate with a focused deferred source, and own animation-hook registrations reversibly. Make OpenAL construction and teardown transactional so every device, context, source, and buffer prefix is retryable without replay.

tests/AcDream.App.Tests/Composition/AnimationHookRegistrationSetTests.cs

@@ -0,0 +1,77 @@
+using System.Numerics;
+using AcDream.App.Composition;
+using AcDream.Core.Physics;
+using DatReaderWriter.Types;
+
+namespace AcDream.App.Tests.Composition;
+
+public sealed class AnimationHookRegistrationSetTests
+{
+    [Fact]
+    public void CleanupUnregistersInReverseAndNeverReplaysSuccessfulEdges()
+    {
+        var calls = new List<string>();
+        var first = new Sink("first");
+        var second = new Sink("second");
+        var third = new Sink("third");
+        bool failSecond = true;
+        var registrations = new AnimationHookRegistrationSet(
+            sink => calls.Add($"add:{((Sink)sink).Name}"),
+            sink =>
+            {
+                string name = ((Sink)sink).Name;
+                calls.Add($"remove:{name}");
+                if (name == "second" && failSecond)
+                    throw new InvalidOperationException("synthetic removal failure");
+            });
+        registrations.Register(first);
+        registrations.Register(second);
+        registrations.Register(third);
+
+        Assert.Throws<AggregateException>(registrations.Dispose);
+        Assert.False(registrations.IsCleanupComplete);
+        failSecond = false;
+        registrations.Dispose();
+        registrations.Dispose();
+
+        Assert.True(registrations.IsCleanupComplete);
+        Assert.Equal(
+            [
+                "add:first", "add:second", "add:third",
+                "remove:third", "remove:second", "remove:first",
+                "remove:second",
+            ],
+            calls);
+    }
+
+    [Fact]
+    public void DuplicateRegistrationIsIdempotentAndClosedSetRejectsNewEdges()
+    {
+        int adds = 0;
+        int removes = 0;
+        var sink = new Sink("only");
+        var registrations = new AnimationHookRegistrationSet(
+            _ => adds++,
+            _ => removes++);
+
+        registrations.Register(sink);
+        registrations.Register(sink);
+        registrations.Dispose();
+
+        Assert.Equal(1, adds);
+        Assert.Equal(1, removes);
+        Assert.Throws<ObjectDisposedException>(() =>
+            registrations.Register(new Sink("late")));
+    }
+
+    private sealed class Sink(string name) : IAnimationHookSink
+    {
+        public string Name { get; } = name;
+        public void OnHook(
+            uint entityId,
+            Vector3 entityWorldPosition,
+            AnimationHook hook)
+        {
+        }
+    }
+}