test(e2e): align test default menu to Top; make legacy specs explicit (#5746)

## Summary
UseNewMenu has been defaulted to Top in the app for over a year;
Playwright’s test default lagged behind. This PR aligns the test default
with reality and keeps legacy specs stable.

## Changes
- tests(e2e): default to 'Top' via fixture; specs that previously relied
on the old implicit default now explicitly set 'Comfy.UseNewMenu' to
'Disabled'.
- docs(browser-tests): remove outdated README note suggesting tests set
'Top' manually.

## Review Focus
- Intentional uses of 'Top' and 'Bottom' remain unchanged.
- Confirm ComfyPage default remains 'Top' (see
browser_tests/fixtures/ComfyPage.ts).

## Screenshots (if applicable)
N/A

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5746-test-e2e-align-test-default-menu-to-Top-make-legacy-specs-explicit-2786d73d365081218d06c1346f3ae18e)
by [Unito](https://www.unito.io)

---------

Co-authored-by: github-actions <github-actions@github.com>

browser_tests/fixtures/ComfyPage.ts

@@ -1643,7 +1643,7 @@ export const comfyPageFixture = base.extend<{
 
     try {
       await comfyPage.setupSettings({
-        'Comfy.UseNewMenu': 'Disabled',
+        'Comfy.UseNewMenu': 'Top',
         // Hide canvas menu/info/selection toolbox by default.
         'Comfy.Graph.CanvasInfo': false,
         'Comfy.Graph.CanvasMenu': false,