fix: make flaky legacy prompt dialog test use locator rather than snapshot (#7371)

## Summary

Fix the flakiness of [this
test](https://fad8c753.comfyui-playwright-chromium.pages.dev/#?testId=967c1c643b6ca86a362c-8b516e2c224693bf7657)
by converting it from using snapshots to just normal locators.

The LiteGraph prompt that opens when click canvas widgets
(number/string) is still the raw DOM dialog created by
`LGraphCanvas.prototype.prompt`. That implementation wires its "click
outside to close" handler inside a `setTimeout` and ignores outside
clicks for ~256 ms after the dialog appears. It also never updates Vue
state or exposes a ready attribute/event we can observe from Playwright.

Because the UI offers no deterministic signal, using a short intentional
wait that matches the real guard is reasonable. We assert the dialog
becomes visible, call `await comfyPage.delay(300)` (just longer than the
256 ms guard), and then click outside. Without this wait the closing
click fires before the handler exists, so the dialog remains visible and
the test flakes. Until the widget exposes a ready hook, this scoped
delay is the most reliable approach and stays within Playwright guidance
("only sleep when there is no observable condition to await").


┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7371-fix-make-flaky-legacy-prompt-dialog-test-use-locator-rather-than-snapshot-2c66d73d36508125b388e68861d7cd28)
by [Unito](https://www.unito.io)

browser_tests/tests/interaction.spec.ts

@@ -306,14 +306,16 @@ test.describe('Node Interaction', () => {
     await comfyPage.canvas.click({
       position: numberWidgetPos
     })
-    await expect(comfyPage.canvas).toHaveScreenshot('prompt-dialog-opened.png')
+    const legacyPrompt = comfyPage.page.locator('.graphdialog')
+    await expect(legacyPrompt).toBeVisible()
+    await comfyPage.delay(300)
     await comfyPage.canvas.click({
       position: {
         x: 10,
         y: 10
       }
     })
-    await expect(comfyPage.canvas).toHaveScreenshot('prompt-dialog-closed.png')
+    await expect(legacyPrompt).toBeHidden()
   })
 
   test('Can close prompt dialog with canvas click (text widget)', async ({
@@ -327,18 +329,16 @@ test.describe('Node Interaction', () => {
     await comfyPage.canvas.click({
       position: textWidgetPos
     })
-    await expect(comfyPage.canvas).toHaveScreenshot(
-      'prompt-dialog-opened-text.png'
-    )
+    const legacyPrompt = comfyPage.page.locator('.graphdialog')
+    await expect(legacyPrompt).toBeVisible()
+    await comfyPage.delay(300)
     await comfyPage.canvas.click({
       position: {
         x: 10,
         y: 10
       }
     })
-    await expect(comfyPage.canvas).toHaveScreenshot(
-      'prompt-dialog-closed-text.png'
-    )
+    await expect(legacyPrompt).toBeHidden()
   })
 
   test('Can double click node title to edit', async ({ comfyPage }) => {