refactor(tests): enhance agent activity tests for new flow editor

### Summary
- Updated `agent-activity.spec.ts` to utilize the new flow editor's methods for adding blocks, improving test reliability and alignment with the current UI.
- Refactored `BuildPage` methods in `build.page.ts` to streamline block interactions and improve visibility checks, ensuring tests accurately reflect user actions.

### Impact
These changes enhance the robustness of the test suite, ensuring it remains functional and relevant with the latest UI updates.

### Testing
- Verified that all updated tests pass successfully, confirming the new interactions work as intended.

autogpt_platform/frontend/src/tests/pages/build.page.ts

@@ -27,7 +27,7 @@ export class BuildPage extends BasePage {
       await this.page
         .getByRole("button", { name: "Skip Tutorial", exact: true })
         .click({ timeout: 3000 });
-    } catch (_error) {
+    } catch (error) {
       console.info("Tutorial not shown or already dismissed");
     }
   }