[feat] Restore group node conversion menu with deprecated label (#4967)

## Summary
- Partially reverts commit c84218d6 to restore group node functionality
in context menus
- Adds "(Deprecated)" label to indicate the feature is deprecated
- Fixes TypeError when right-clicking on group nodes
- Re-enables tests that were disabled when the feature was removed

## Changes
1. **Restored context menu options** - Added back "Convert to Group Node
(Deprecated)" and "Manage Group Nodes" menu items
2. **Fixed null reference error** - Added null-safe operator to prevent
errors when right-clicking group nodes
3. **Re-enabled tests** - Restored 7 tests that were disabled in commit
586f8824

## Test plan
- [x] Right-click on canvas → verify "Convert to Group Node
(Deprecated)" appears
- [x] Right-click on nodes → verify the same menu option appears
- [x] Select multiple nodes and use the menu option → verify conversion
works
- [x] Right-click on group nodes → verify no errors occur
- [x] Run browser tests → verify all re-enabled tests pass

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-4967-feat-Restore-group-node-conversion-menu-with-deprecated-label-24e6d73d36508149a6f2dbef47223e94)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: github-actions <github-actions@github.com>

browser_tests/tests/rightClickMenu.spec.ts

@@ -24,11 +24,11 @@ test.describe('Canvas Right Click Menu', () => {
     await expect(comfyPage.canvas).toHaveScreenshot('add-group-group-added.png')
   })
 
-  test.skip('Can convert to group node', async ({ comfyPage }) => {
+  test('Can convert to group node', async ({ comfyPage }) => {
     await comfyPage.select2Nodes()
     await expect(comfyPage.canvas).toHaveScreenshot('selected-2-nodes.png')
     await comfyPage.rightClickCanvas()
-    await comfyPage.clickContextMenuItem('Convert to Group Node')
+    await comfyPage.clickContextMenuItem('Convert to Group Node (Deprecated)')
     await comfyPage.promptDialogInput.fill('GroupNode2CLIP')
     await comfyPage.page.keyboard.press('Enter')
     await comfyPage.promptDialogInput.waitFor({ state: 'hidden' })