fix(items): complete retail corpse looting feedback

Route corpse Use through the shared ItemHolder policy so Stuck corpses open instead of being sent as pickup requests. Restore the framed, horizontally resizable external-container strip and use a compact initial width. Port retail's target-list pending item projection so loot is marked in the chosen inventory slot without changing canonical ownership before the server confirms.

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

src/AcDream.App/UI/UiItemSlot.cs

@@ -144,9 +144,17 @@ public class UiItemSlot : UiElement
         // ItemList_BeginDrag ghosts physical lists, but explicitly excludes shortcut lists
         // (along with vendor/salvage lists, which acdream does not model as ItemDragSource).
         // Keep the source's full cell icon in place and reveal the authored grey mesh over it.
-        _waiting = active && ItemId != 0 && SourceKind != ItemDragSource.ShortcutBar;
+        SetWaitingState(active && SourceKind != ItemDragSource.ShortcutBar);
     }
 
+    /// <summary>
+    /// Apply retail's <c>m_elem_Icon_Ghosted</c> waiting presentation independently
+    /// of pointer ownership. Destination ItemLists use this for their temporary
+    /// <c>m_pendingItem</c> inserted by <c>HandleDropRelease @ 0x004E4790</c>.
+    /// </summary>
+    internal void SetWaitingState(bool waiting)
+        => _waiting = waiting && ItemId != 0;
+
     /// <summary>An OCCUPIED slot is a drag source — a press-and-move picks up the item
     /// rather than moving the toolbar window. An EMPTY slot is NOT a drag source, so a
     /// press-and-move there falls through to the IA-12 whole-window-drag, keeping the bar