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/BuilderSaveAsHelper.ts

@@ -0,0 +1,78 @@
+import type { Locator, Page } from '@playwright/test'
+
+import type { ComfyPage } from '../ComfyPage'
+
+export class BuilderSaveAsHelper {
+  constructor(private readonly comfyPage: ComfyPage) {}
+
+  private get page(): Page {
+    return this.comfyPage.page
+  }
+
+  /** The save-as dialog (scoped by aria-labelledby). */
+  get dialog(): Locator {
+    return this.page.locator('[aria-labelledby="builder-save"]')
+  }
+
+  /** The post-save success dialog (scoped by aria-labelledby). */
+  get successDialog(): Locator {
+    return this.page.locator('[aria-labelledby="builder-save-success"]')
+  }
+
+  get title(): Locator {
+    return this.dialog.getByText('Save as')
+  }
+
+  get radioGroup(): Locator {
+    return this.dialog.getByRole('radiogroup')
+  }
+
+  get nameInput(): Locator {
+    return this.dialog.getByRole('textbox')
+  }
+
+  viewTypeRadio(viewType: 'App' | 'Node graph'): Locator {
+    return this.dialog.getByRole('radio', { name: viewType })
+  }
+
+  get saveButton(): Locator {
+    return this.dialog.getByRole('button', { name: 'Save' })
+  }
+
+  get successMessage(): Locator {
+    return this.successDialog.getByText('Successfully saved')
+  }
+
+  get viewAppButton(): Locator {
+    return this.successDialog.getByRole('button', { name: 'View app' })
+  }
+
+  get closeButton(): Locator {
+    return this.successDialog
+      .getByRole('button', { name: 'Close', exact: true })
+      .filter({ hasText: 'Close' })
+  }
+
+  /** The X button to dismiss the success dialog without any action. */
+  get dismissButton(): Locator {
+    return this.successDialog.locator('button.p-dialog-close-button')
+  }
+
+  get exitBuilderButton(): Locator {
+    return this.successDialog.getByRole('button', { name: 'Exit builder' })
+  }
+
+  get overwriteDialog(): Locator {
+    return this.page.getByRole('dialog', { name: 'Overwrite existing file?' })
+  }
+
+  get overwriteButton(): Locator {
+    return this.overwriteDialog.getByRole('button', { name: 'Overwrite' })
+  }
+
+  async fillAndSave(workflowName: string, viewType: 'App' | 'Node graph') {
+    await this.nameInput.fill(workflowName)
+    await this.viewTypeRadio(viewType).click()
+    await this.saveButton.click()
+  }
+}