feat(D.5.1): faithful item-icon type-default underlay (EnumIDMap 0x10000004) — opaque icon backing

Retail IconData::RenderIcons (decomp 407524) builds the icon layer stack bottom→top:
type-default underlay (OPAQUE, Blit_Normal) first, then custom underlay, base icon,
custom overlay.  acdream's IconComposer omitted the type-default underlay, leaving
filled toolbar slots with a transparent background.

Resolution via the two-level EnumIDMap chain that retail uses (DBCache::GetDIDFromEnum
0x413940): Portal.Header.MasterMapId (0x25000000) → master[0x10000004] → submap DID
(0x25000008) → submap[LSB(itemType)+1] → 0x06 RenderSurface underlay DID.  Golden
values confirmed against the live dats: MeleeWeapon→0x060011CB, Armor→0x060011CF,
Clothing→0x060011F3, Jewelry→0x060011D5, None(fallback 0x21)→0x060011D4.

Changes:
- IconComposer: add ResolveUnderlayDid(ItemType)/EnsureUnderlaySubMap (memoised);
  widen cache key from (uint,uint,uint)→(uint,uint,uint,uint); GetIcon gains ItemType
  param and prepends the opaque underlay as layer 0 (Compose sizes to it → fully opaque)
- ToolbarController: widen _iconIds Func from 3-arg to 4-arg; Populate passes item.Type
- GameWindow: update toolbar mount lambda to 4-arg form
- Tests: update ToolbarController test stubs to (_,_,_,_); add
  Compose_opaqueUnderlayFirst_resultIsFullyOpaque (dat-free) and
  ResolveUnderlayDid_goldenValues_matchDat (dat-gated, skip when dats absent)

No divergence-register row existed for this omission; none added (fully ported now).

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

tests/AcDream.App.Tests/UI/Layout/ToolbarControllerTests.cs

@@ -53,7 +53,7 @@ public class ToolbarControllerTests
         { new(Index: 0, ObjectGuid: 0x5001u, SpellId: 0, Layer: 0) };
 
         ToolbarController.Bind(layout, repo, () => shortcuts,
-            iconIds: (_,_,_) => 0x77u, useItem: _ => { });
+            iconIds: (_,_,_,_) => 0x77u, useItem: _ => { });
 
         Assert.Equal(0x5001u, slots[Row1[0]].Cell.ItemId);
         Assert.Equal(0x77u,   slots[Row1[0]].Cell.IconTexture);
@@ -69,7 +69,7 @@ public class ToolbarControllerTests
         { new(Index: 2, ObjectGuid: 0x5002u, SpellId: 0, Layer: 0) };
 
         ToolbarController.Bind(layout, repo, () => shortcuts,
-            iconIds: (_,_,_) => 0x88u, useItem: _ => { });
+            iconIds: (_,_,_,_) => 0x88u, useItem: _ => { });
         Assert.Equal(0u, slots[Row1[2]].Cell.ItemId); // not bound yet
 
         repo.AddOrUpdate(new ItemInstance { ObjectId = 0x5002u, WeenieClassId = 1u, IconId = 0x06005678u });
@@ -88,7 +88,7 @@ public class ToolbarControllerTests
         uint used = 0;
 
         ToolbarController.Bind(layout, repo, () => shortcuts,
-            iconIds: (_,_,_) => 0x77u, useItem: g => used = g);
+            iconIds: (_,_,_,_) => 0x77u, useItem: g => used = g);
         // UiEvent is a positional record struct: (SourceId, Target, Type, Data0..3, Payload)
         slots[Row1[0]].Cell.OnEvent(new UiEvent(0u, null, UiEventType.MouseDown));
 
@@ -110,7 +110,7 @@ public class ToolbarControllerTests
 
         ToolbarController.Bind(layout, repo,
             () => Array.Empty<PlayerDescriptionParser.ShortcutEntry>(),
-            iconIds: (_,_,_) => 0u, useItem: _ => { });
+            iconIds: (_,_,_,_) =>0u, useItem: _ => { });
 
         // Only peace indicator (index 0 = 0x10000192) is visible.
         Assert.True (indicators[0x10000192u].Visible, "peace indicator should be visible after bind");
@@ -130,7 +130,7 @@ public class ToolbarControllerTests
 
         var ctrl = ToolbarController.Bind(layout, repo,
             () => Array.Empty<PlayerDescriptionParser.ShortcutEntry>(),
-            iconIds: (_,_,_) => 0u, useItem: _ => { });
+            iconIds: (_,_,_,_) =>0u, useItem: _ => { });
 
         ctrl.SetCombatMode(CombatMode.Melee);
 
@@ -152,7 +152,7 @@ public class ToolbarControllerTests
 
         ToolbarController.Bind(layout, repo,
             () => Array.Empty<PlayerDescriptionParser.ShortcutEntry>(),
-            iconIds: (_,_,_) => 0u, useItem: _ => { },
+            iconIds: (_,_,_,_) =>0u, useItem: _ => { },
             combatState: combat);
 
         // Initially NonCombat after bind.