fix(rack): prevent dragged module unmounting to fix dnd-kit drop

client/src/components/rack/RackColumn.tsx

@@ -12,13 +12,11 @@ import { useRackStore } from '../../store/useRackStore';
 
 interface RackColumnProps {
   rack: Rack;
-  /** ID of the module currently being dragged — render its slots as droppable ghosts. */
-  draggingModuleId?: string | null;
   /** Slot currently hovered by a drag — passed down to RackSlot for blue highlight. */
   hoverSlot?: { rackId: string; uPosition: number } | null;
 }
 
-export function RackColumn({ rack, draggingModuleId, hoverSlot }: RackColumnProps) {
+export function RackColumn({ rack, hoverSlot }: RackColumnProps) {
   const { deleteRack } = useRackStore();
   const [confirmDeleteOpen, setConfirmDeleteOpen] = useState(false);
   const [deleting, setDeleting] = useState(false);
@@ -98,9 +96,7 @@ export function RackColumn({ rack, draggingModuleId, hoverSlot }: RackColumnProp
             ))}
           </div>
 
-          {rack.modules
-            .filter((module) => module.id !== draggingModuleId)
-            .map((module) => (
+          {rack.modules.map((module) => (
               <div
                 key={module.id}
                 className="absolute left-0 right-0 z-10"

client/src/components/rack/RackPlanner.tsx

@@ -259,7 +259,6 @@ export function RackPlanner() {
                     <RackColumn
                       key={rack.id}
                       rack={rack}
-                      draggingModuleId={draggingModuleId}
                       hoverSlot={hoverSlot}
                     />
                   ))}