Add onRangeSelect handler for multi-selection support

frontend/src/pages/Dms.tsx

@@ -212,6 +212,11 @@ export function DmsPage() {
     });
   }, []);
 
+  // Handle range select (Shift+Click or rubber-band)
+  const handleRangeSelect = useCallback((fileIds: string[]) => {
+    setSelectedFileIds(new Set(fileIds));
+  }, []);
+
   // Handle confirm delete
   const handleConfirmDelete = useCallback(async () => {
     if (!deleteTarget) return;
@@ -545,6 +550,7 @@ export function DmsPage() {
             sortBy={sortBy}
             sortOrder={sortOrder}
             onSortChange={handleSortChange}
+            onRangeSelect={handleRangeSelect}
           />
         </ResizablePanel>
 
@@ -638,6 +644,7 @@ export function DmsPage() {
               sortBy={sortBy}
               sortOrder={sortOrder}
               onSortChange={handleSortChange}
+              onRangeSelect={handleRangeSelect}
             />
           </div>
         )}