ISSUE 7: add delete functionality

src/components/DockBuilder/DockBuilder.jsx

@@ -594,7 +594,13 @@ export const DockBuilder = () => {
   };
 
   const onDeleteSelection = () => {
-    // TODO: Delete selection
+    const activeObject = editorMemo.getActiveObject();
+    if (activeObject) {
+      editorMemo.remove(activeObject);
+      editorMemo.discardActiveObject();
+      editorMemo.renderAll();
+      updateModifications(true, { target: activeObject });
+    }
   };
 
   const addLines = useCallback(() => {