Add the drop zone arbiter, still without consumers

app/MindWork AI Studio/Routes.razor

@@ -1,4 +1,5 @@
-@using Microsoft.AspNetCore.Components.Routing
+@using AIStudio.Components
+@using Microsoft.AspNetCore.Components.Routing
 @using MudBlazor
 
 <Router AppAssembly="typeof(Program).Assembly">
@@ -10,4 +11,8 @@
 
 <MudDialogProvider />
 <MudPopoverProvider />
-<MudSnackbarProvider />
+<MudSnackbarProvider />
+
+@* Outside the router on purpose: which drop zone a drop belongs to is a question of the whole
+   session, not of the current page. *@
+<DropZoneArbiter />