fix(studio): Task 4 — bind PaperdollController + wire empty-slot sprites

FixtureProvider.Populate for 0x21000023 was binding only
InventoryController and omitting PaperdollController, so the
~21 equip slots rendered empty even though sample equipped items
existed in the table.  Also, the three per-list empty-slot
sprites were not being resolved from the dat (contentsEmpty /
sideBagEmpty / mainPackEmpty all defaulted to 0), so the slot cells
had no background art.

Fixes:
- FixtureProvider.Populate gains a DatCollection dats param
  (mirrors the GameWindow.OnLoad lookup at line 2233-2235).
  The 0x21000023 case now resolves all three empty sprites via
  ItemListCellTemplate.ResolveEmptySprite and passes them to
  InventoryController.Bind.
- PaperdollController.Bind is now called after InventoryController
  in the same 0x21000023 case, matching GameWindow:2257-2265
  (same layout subtree, contentsEmpty as the equip-slot placeholder,
  sendWield: null since there is no live session in the studio).
- StudioWindow.OnLoad passes _dats! to the updated Populate signature.

SampleData.AddEquipped was already correct: MoveItem(guid, PlayerGuid,
-1, equipMask) at ClientObjectTable.cs:134 sets
CurrentlyEquippedLocation = newEquipLocation and calls Reindex which
places the item in _containerIndex[PlayerGuid].  No SampleData change
needed.

Tests: 2 new assertions in FixtureProviderTests —
  sideBags_matchInventoryControllerFilter (Type.HasFlag(Container)
  || ItemsCapacity > 0 filter must match both bags) and
  equippedItems_retainLocationAndAreInContents (equipped items have
  CurrentlyEquippedLocation != None AND appear in GetContents so the
  paperdoll controller can find them).  604 pass / 2 skip / 0 fail.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/AcDream.App/Studio/FixtureProvider.cs

@@ -3,6 +3,7 @@ using AcDream.App.UI;
 using AcDream.App.UI.Layout;
 using AcDream.Core.Items;
 using AcDream.Core.Net.Messages;
+using DatReaderWriter;
 
 namespace AcDream.App.Studio;
 
@@ -41,11 +42,14 @@ public static class FixtureProvider
     /// and <see cref="RenderStack.VitalsDatFont"/>).</param>
     /// <param name="objects">A <see cref="ClientObjectTable"/> already seeded by
     /// <see cref="SampleData.BuildObjectTable"/>.</param>
+    /// <param name="dats">The live DAT collection used to resolve per-list empty-slot sprites
+    /// (same lookup GameWindow.OnLoad performs for the production binding).</param>
     public static void Populate(
         uint layoutId,
         ImportedLayout layout,
         RenderStack stack,
-        ClientObjectTable objects)
+        ClientObjectTable objects,
+        DatCollection dats)
     {
         switch (layoutId)
         {
@@ -74,15 +78,41 @@ public static class FixtureProvider
                     sendRemoveShortcut: null);
                 break;
 
-            case 0x21000023u:   // inventory
+            case 0x21000023u:   // inventory + paperdoll
+            {
+                // Resolve the per-list empty-slot art from the dat cell template, matching the
+                // exact lookup GameWindow.OnLoad performs (UIElement_ItemList::InternalCreateItem
+                // 0x004e3570 → attr 0x1000000e → catalog 0x21000037 → ItemSlot_Empty).
+                uint contentsEmpty  = ItemListCellTemplate.ResolveEmptySprite(dats, 0x21000021u, 0x100001C6u);
+                uint sideBagEmpty   = ItemListCellTemplate.ResolveEmptySprite(dats, 0x21000022u, 0x100001CAu);
+                uint mainPackEmpty  = ItemListCellTemplate.ResolveEmptySprite(dats, 0x21000022u, 0x100001C9u);
+
+                var iconIds = MakeIconIds(stack);
+
                 InventoryController.Bind(
                     layout,
                     objects,
-                    playerGuid: () => SampleData.PlayerGuid,
-                    iconIds:    MakeIconIds(stack),
-                    strength:   () => 100,
-                    datFont:    stack.VitalsDatFont);
+                    playerGuid:             () => SampleData.PlayerGuid,
+                    iconIds:                iconIds,
+                    strength:               () => 100,
+                    datFont:                stack.VitalsDatFont,
+                    contentsEmptySprite:    contentsEmpty,
+                    sideBagEmptySprite:     sideBagEmpty,
+                    mainPackEmptySprite:    mainPackEmpty);
+
+                // Bind the paperdoll equip slots (same imported subtree as the inventory).
+                // Mirrors GameWindow:2257-2265: PaperdollController.Bind with contentsEmpty as
+                // emptySlotSprite (each slot shows the same square-frame placeholder as the grid).
+                PaperdollController.Bind(
+                    layout,
+                    objects,
+                    playerGuid:       () => SampleData.PlayerGuid,
+                    iconIds:          iconIds,
+                    sendWield:        null,       // no live session in the studio
+                    emptySlotSprite:  contentsEmpty,
+                    datFont:          stack.VitalsDatFont);
                 break;
+            }
 
             default:
                 // Unknown layout — no-op; the panel renders structurally.

src/AcDream.App/Studio/StudioWindow.cs

@@ -130,7 +130,7 @@ public sealed class StudioWindow : IDisposable
             {
                 uint layoutId = _opts.LayoutId ?? 0x2100006Cu;
                 _objects = SampleData.BuildObjectTable();
-                FixtureProvider.Populate(layoutId, _source.CurrentLayout, _stack, _objects);
+                FixtureProvider.Populate(layoutId, _source.CurrentLayout, _stack, _objects, _dats);
             }
         }
         else