fix(editor): textarea not focusing in AI panel (#11429)

Closes: [BS-3006](https://linear.app/affine-design/issue/BS-3006/insider上面，圈选yuan素后，ad-hoc的ai对话框焦点控制有大问题（无法对焦，总是会跳走）)

tests/affine-cloud-copilot/e2e/chat-with/text.spec.ts

@@ -127,4 +127,15 @@ test.describe('AIChatWith/Text', () => {
     const content = await utils.editor.getEditorContent(page);
     expect(content).toBe('Apple');
   });
+
+  test('should focus on textarea', async ({ page, utils }) => {
+    await utils.editor.askAIWithText(page, 'Apple');
+
+    const textarea = await utils.editor.whatAreYourThoughts(page, 'Coffee');
+
+    await expect(textarea).toBeFocused();
+
+    const value = await textarea.inputValue();
+    expect(value).toBe('Coffee');
+  });
 });