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');
+  });
 });

tests/affine-cloud-copilot/e2e/utils/editor-utils.ts

@@ -582,4 +582,12 @@ export class EditorUtils {
       ),
     } as const;
   }
+
+  public static async whatAreYourThoughts(page: Page, text: string) {
+    const textarea = page.locator(
+      'affine-ai-panel-widget .ai-panel-container textarea'
+    );
+    await textarea.fill(text);
+    return textarea;
+  }
 }