feat(items): port retail external-container looting

Add the ClientUISystem ground-object lifecycle, authoritative root and nested ViewContents projections, replacement and close semantics, and the DAT-authored gmExternalContainerUI strip for chests and corpses.

Route double-click loot and full or partial drag transfers through the shared retail item policy without optimistic external ownership. Remove the incorrect NoLongerViewingContents behavior from owned side packs and retire AP-106/#196.

Release build succeeds and all 5,875 tests pass with five intentional skips.

Co-authored-by: OpenAI Codex <codex@openai.com>

tests/AcDream.Core.Net.Tests/GameEventWiringTests.cs

@@ -950,6 +950,45 @@ public sealed class GameEventWiringTests
         Assert.Equal(0u, items.Get(0x50000A01u)!.ContainerId);
     }
 
+    [Fact]
+    public void WireAll_ExternalContainer_FiltersNestedViewsAndAppliesAuthoritativeClose()
+    {
+        var dispatcher = new GameEventDispatcher();
+        var items = new ClientObjectTable();
+        var external = new ExternalContainerState();
+        GameEventWiring.WireAll(
+            dispatcher,
+            items,
+            new CombatState(),
+            new Spellbook(),
+            new ChatLog(),
+            externalContainers: external);
+        external.RequestOpen(0x70000001u);
+
+        DispatchViewContents(
+            dispatcher,
+            0x70000001u,
+            new uint[] { 0x60000001u, 0x70000002u });
+        DispatchViewContents(dispatcher, 0x70000002u, new uint[] { 0x60000002u });
+
+        Assert.Equal(0x70000001u, external.CurrentContainerId);
+        Assert.Equal(
+            new uint[] { 0x60000001u, 0x70000002u },
+            items.GetContents(0x70000001u));
+        Assert.Equal(new uint[] { 0x60000002u }, items.GetContents(0x70000002u));
+
+        byte[] closePayload = new byte[4];
+        BinaryPrimitives.WriteUInt32LittleEndian(closePayload, 0x70000001u);
+        var close = GameEventEnvelope.TryParse(
+            WrapEnvelope(GameEventType.CloseGroundContainer, closePayload));
+        dispatcher.Dispatch(close!.Value);
+
+        Assert.Equal(0u, external.CurrentContainerId);
+        Assert.Empty(items.GetContents(0x70000001u));
+        Assert.NotNull(items.Get(0x60000001u));
+        Assert.Empty(items.GetContents(0x70000002u));
+    }
+
     private static void DispatchViewContents(GameEventDispatcher d, uint containerGuid, uint[] itemGuids)
     {
         byte[] payload = new byte[8 + itemGuids.Length * 8];