test/refactor: App mode - Refactor & Save As tests (#10680)

## Summary

Adds e2e Save As tests for #10679.
Refactors tests to remove getByX and other locators in tests to instead
be in fixtures.

## Changes

- **What**: 
- extract app mode fixtures
- add test ids where required
- add new tests

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-10680-test-refactor-App-mode-Refactor-Save-As-tests-3316d73d3650815b9d49ccfbb6d54416)
by [Unito](https://www.unito.io)

browser_tests/fixtures/helpers/BuilderStepsHelper.ts

@@ -0,0 +1,30 @@
+import type { Locator, Page } from '@playwright/test'
+
+import type { ComfyPage } from '../ComfyPage'
+
+export class BuilderStepsHelper {
+  constructor(private readonly comfyPage: ComfyPage) {}
+
+  private get page(): Page {
+    return this.comfyPage.page
+  }
+
+  get toolbar(): Locator {
+    return this.page.getByRole('navigation', { name: 'App Builder' })
+  }
+
+  async goToInputs() {
+    await this.toolbar.getByRole('button', { name: 'Inputs' }).click()
+    await this.comfyPage.nextFrame()
+  }
+
+  async goToOutputs() {
+    await this.toolbar.getByRole('button', { name: 'Outputs' }).click()
+    await this.comfyPage.nextFrame()
+  }
+
+  async goToPreview() {
+    await this.toolbar.getByRole('button', { name: 'Preview' }).click()
+    await this.comfyPage.nextFrame()
+  }
+}