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/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