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/BuilderFooterHelper.ts

@@ -0,0 +1,69 @@
+import type { Locator, Page } from '@playwright/test'
+
+import type { ComfyPage } from '../ComfyPage'
+import { TestIds } from '../selectors'
+
+export class BuilderFooterHelper {
+  constructor(private readonly comfyPage: ComfyPage) {}
+
+  private get page(): Page {
+    return this.comfyPage.page
+  }
+
+  get nav(): Locator {
+    return this.page.getByTestId(TestIds.builder.footerNav)
+  }
+
+  get exitButton(): Locator {
+    return this.buttonByName('Exit app builder')
+  }
+
+  get nextButton(): Locator {
+    return this.buttonByName('Next')
+  }
+
+  get backButton(): Locator {
+    return this.buttonByName('Back')
+  }
+
+  get saveButton(): Locator {
+    return this.page.getByTestId(TestIds.builder.saveButton)
+  }
+
+  get saveAsButton(): Locator {
+    return this.page.getByTestId(TestIds.builder.saveAsButton)
+  }
+
+  get saveAsChevron(): Locator {
+    return this.page.getByTestId(TestIds.builder.saveAsChevron)
+  }
+
+  get opensAsPopover(): Locator {
+    return this.page.getByTestId(TestIds.builder.opensAs)
+  }
+
+  private buttonByName(name: string): Locator {
+    return this.nav.getByRole('button', { name })
+  }
+
+  async next() {
+    await this.nextButton.click()
+    await this.comfyPage.nextFrame()
+  }
+
+  async back() {
+    await this.backButton.click()
+    await this.comfyPage.nextFrame()
+  }
+
+  async exitBuilder() {
+    await this.exitButton.click()
+    await this.comfyPage.nextFrame()
+  }
+
+  async openSaveAsFromChevron() {
+    await this.saveAsChevron.click()
+    await this.page.getByRole('menuitem', { name: 'Save as' }).click()
+    await this.comfyPage.nextFrame()
+  }
+}