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/drag-handle.spec.ts

@@ -216,3 +216,33 @@ test('should keep relative order of new note when a block is dragged from note t
   await waitNextFrame(page);
   await assertRichTexts(page, ['3', '5', '6', '7', '9']);
 });
+
+test('drag handle should work when hover on the background of a selected edgeless note', async ({
+  page,
+}) => {
+  await enterPlaygroundRoom(page);
+  await initEmptyEdgelessState(page);
+  await focusRichText(page);
+  await type(page, 'hello');
+  await switchEditorMode(page);
+  await page.mouse.dblclick(CENTER_X, CENTER_Y);
+  // wait for the note animation
+  await waitNextFrame(page, 400);
+
+  const noteRect = await page.locator('affine-edgeless-note').boundingBox();
+  assertRectExist(noteRect);
+
+  const noteBackgroundRect = await page
+    .locator('edgeless-note-background')
+    .boundingBox();
+  assertRectExist(noteBackgroundRect);
+
+  const paragraphRect = await page.locator('affine-paragraph').boundingBox();
+  assertRectExist(paragraphRect);
+
+  // move to the area between note background and note block and before the paragraph
+  const x = (noteRect.x + noteBackgroundRect.x) / 2;
+  const y = paragraphRect.y + paragraphRect.height / 2;
+  await page.mouse.move(x, y, { steps: 2 });
+  await expect(page.locator('.affine-drag-handle-container')).toBeVisible();
+});

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;
     });
   };