feat(core): add web search tool and reasoning params (#11912)

Close [AI-60](https://linear.app/affine-design/issue/AI-60).

### What changed?
- Add Exa web search tool
- Add reasoning params

tests/affine-cloud-copilot/e2e/utils/chat-panel-utils.ts

@@ -37,9 +37,6 @@ export class ChatPanelUtils {
     }
     await page.getByTestId('sidebar-tab-chat').click();
     await expect(page.getByTestId('sidebar-tab-content-chat')).toBeVisible();
-    // TODO: remove this
-    // after network search is disabled by default
-    await this.disableNetworkSearch(page);
   }
 
   public static async closeChatPanel(page: Page) {