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>

e2e/test_article_detail.py

@@ -66,8 +66,6 @@ def test_copy_link_button_updates_text(page: Page, base_url: str) -> None:
     _go_to_article(page, base_url)
     copy_btn = page.get_by_role("button", name="Copy link")
     expect(copy_btn).to_be_visible()
-    # Grant clipboard permission and click
-    page.context.grant_permissions(["clipboard-read", "clipboard-write"])
     copy_btn.click()
-    # Button text should change to "Copied" after click
+    # Clipboard polyfill in conftest ensures writeText resolves; button shows "Copied"
     expect(copy_btn).to_have_text("Copied")