fix: resolve 5 E2E test failures from first CI run

- test_homepage_title_contains_brand: to_have_title() requires a string or
  regex, not a lambda; switch to re.compile('No Hype AI')
- test_granular_preferences_save_dismisses_banner: wrong element clicked to
  open <details>; use 'details summary' locator directly
- test_subscribe_invalid_email_shows_error: browser HTML5 email validation
  swallows the submit event before the JS handler fires; add 'novalidate' via
  evaluate() so the fetch still runs and the server returns 400
- test_copy_link_button_updates_text: clipboard API unavailable in headless
  Docker; add polyfill + pre-grant permissions in conftest page fixture so
  the JS success path runs and button text becomes 'Copied'
- test_comments_section_absent_when_disabled: guard against Wagtail's
  add_child() resetting BooleanField defaults by calling an explicit
  .update(comments_enabled=False) + re-setting on the instance before
  save_revision().publish(); also tighten test to assert 200 + correct title

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

apps/core/management/commands/seed_e2e_content.py

@@ -81,6 +81,10 @@ class Command(BaseCommand):
                 comments_enabled=False,
             )
             article_index.add_child(instance=no_comments_article)
+            # Explicitly persist False after add_child (which internally calls save())
+            # to guard against any field reset in the page tree insertion path.
+            ArticlePage.objects.filter(pk=no_comments_article.pk).update(comments_enabled=False)
+            no_comments_article.comments_enabled = False
             no_comments_article.save_revision().publish()
 
         # About page