Prevent all workflow node and edge deletions made through the UI (#9918)

## Old

In the demo, I press the `Delete` key multiple times, and it deletes the
nodes.


https://github.com/user-attachments/assets/75bf84d3-b182-488c-a781-bbe236985142

## New


https://github.com/user-attachments/assets/4ae4f387-e143-4ce8-8140-6cb2c549f5d2

packages/twenty-front/src/modules/workflow/workflow-diagram/components/WorkflowDiagramCanvasBase.tsx

@@ -227,6 +227,10 @@ export const WorkflowDiagramCanvasBase = ({
         edges={edges}
         onNodesChange={handleNodesChange}
         onEdgesChange={handleEdgesChange}
+        onBeforeDelete={async () => {
+          // Abort all non-programmatic deletions
+          return false;
+        }}
         proOptions={{ hideAttribution: true }}
         multiSelectionKeyCode={null}
         nodesFocusable={false}