fix(editor): drag handle disappeard when hover on the extra area between note and its background (#12536)

Close [BS-3391](https://linear.app/affine-design/issue/BS-3391/无法从note中拖出embed-synced-doc到白板)

### Before
can not hover on drag handle

https://github.com/user-attachments/assets/5596538e-e922-4d7f-8188-b719b234f3ee

### After
can hover on drag handle

https://github.com/user-attachments/assets/855743ec-7601-48a8-8453-cd5aa395bd06

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->

## Summary by CodeRabbit

- **Bug Fixes**
	- Improved detection of hovering over notes in edgeless mode, ensuring the drag handle appears correctly when hovering on the background of a selected note.
	- Enhanced background style updates for edgeless notes, providing more accurate visual feedback.

- **Tests**
	- Added a test to verify that the drag handle is visible when hovering over the background of a selected edgeless note.
	- Updated undo/redo tests to improve accuracy of background color evaluation.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

tests/blocksuite/e2e/edgeless/note/undo-redo.spec.ts

@@ -148,7 +148,7 @@ test('undo/redo should work when change note custom background', async ({
   await selectNoteInEdgeless(page, noteId);
 
   const getNoteBackground = async () => {
-    return page.locator('edgeless-note-background > div').evaluate(el => {
+    return page.locator('edgeless-note-background').evaluate(el => {
       return getComputedStyle(el).backgroundColor;
     });
   };