feat(D.5.1): parse item IconOverlay/IconUnderlay from CreateObject -> faithful icon overlay layer

The CreateObject optional-tail walker previously stopped at UseRadius (~20 fields
before IconOverlay). This left ItemInstance.IconOverlayId/IconUnderlayId always 0,
so IconComposer's underlay/overlay layers were never drawn on toolbar icons.

Exact field order verified against ACE WorldObject_Networking.cs:87-219 (the
serializer is the authority; acdream connects to a local ACE server):
  UseRadius → TargetType(u32) → UiEffects(u32) → CombatUse(sbyte) →
  Structure(u16) → MaxStructure(u16) → StackSize(u16) → MaxStackSize(u16) →
  Container(u32) → Wielder(u32) → ValidLocations(u32) →
  CurrentlyWieldedLocation(u32) → Priority(u32) → RadarBlipColor(u8) →
  RadarBehavior(u8) → PScript(u16) → Workmanship(f32) → Burden(u16) →
  Spell(u16) → HouseOwner(u32) → HouseRestrictions(variable RestrictionDB) →
  HookItemTypes(u32) → Monarch(u32) → HookType(u16) →
  IconOverlay(PackedDwordKnownType) ← CAPTURE →
  IconUnderlay from weenieFlags2 bit 0x01 ← CAPTURE

RestrictionDB handled correctly: Version(u32) + OpenStatus(u32) + MonarchId(u32)
+ count(u16) + numBuckets(u16) + count×8 bytes entries. Length-aware skip, not a
fixed constant.

weenieFlags2 is now CAPTURED (not skipped) when IncludesSecondHeader
(objDescFlags bit 0x04000000) is set, so the IconUnderlay bit can be tested.

The entire extended walk is inside try/catch: truncated packets degrade to
IconOverlayId=0 / IconUnderlayId=0 (no overlay drawn), never corrupting.

Threading: CreateObject.Parsed → WorldSession.EntitySpawn → GameWindow
OnLiveEntitySpawned → Items.EnrichItem — both ids thread through all three
seams. EnrichItem extended with optional iconOverlayId + iconUnderlayId params
(defaulted 0, backward-compatible).

No change to IconComposer or ToolbarController (they already consume the ids).

Tests: 4 new CreateObject tests (IconOverlay only, overlay+underlay, no-overlay
regression, intermediate-fields cursor arithmetic). Full suite: 0 failures,
2636 passed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/GameWindow.cs

@@ -2632,7 +2632,11 @@ public sealed class GameWindow : IDisposable
     {
         // D.5.1: enrich a known inventory/equipped item (stubbed from PlayerDescription)
         // with the icon/name/type its CreateObject carries, so the toolbar can render it.
-        Items.EnrichItem(spawn.Guid, spawn.IconId, spawn.Name ?? string.Empty, (AcDream.Core.Items.ItemType)(spawn.ItemType ?? 0));
+        // D.5.1 (2026-06-17): also pass overlay/underlay ids from the extended
+        // WeenieHeader tail so IconComposer composites all icon layers.
+        Items.EnrichItem(spawn.Guid, spawn.IconId, spawn.Name ?? string.Empty,
+            (AcDream.Core.Items.ItemType)(spawn.ItemType ?? 0),
+            spawn.IconOverlayId, spawn.IconUnderlayId);
 
         // Phase A.1 hotfix: live CreateObject handler reads dats extensively
         // (Setup, GfxObj, Surface, SurfaceTexture) to hydrate the spawned