fix: run E2E tests properly with mounted browsers and real postgres

- Mount /opt/playwright-tools/browsers into web container (docker-compose.yml
  and CI docker run) — never download browsers, use the ones on this host
- Set PLAYWRIGHT_BROWSERS_PATH in all container envs (compose + CI)
- Drop 'playwright install chromium' steps from pr-e2e and nightly-e2e jobs
- Bump playwright requirement to ~1.57.0 to match the installed browser builds
- Fix seed_e2e_content: de-duplicate default Site entries left by unit test
  fixtures so Wagtail always routes to the seeded home page
- Fix test_comments_section_absent_when_disabled: use exact=True on heading
  locator to avoid matching 'No Comments Article' h1 as 'Comments' heading
- Fix test_copy_link_button_updates_text: use [data-copy-link] data-attr
  locator (stable across text change) and force-override clipboard.writeText
  via page.evaluate() rather than relying on init_script polyfill

E2E suite verified locally: 34 passed via docker compose exec

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

docker-compose.yml

@@ -7,6 +7,7 @@ services:
              python manage.py runserver 0.0.0.0:8000"
     volumes:
       - .:/app
+      - /opt/playwright-tools/browsers:/opt/playwright-tools/browsers:ro
     ports:
       - "8035:8000"
     environment:
@@ -21,6 +22,7 @@ services:
       EMAIL_BACKEND: django.core.mail.backends.console.EmailBackend
       DEFAULT_FROM_EMAIL: hello@nohypeai.com
       NEWSLETTER_PROVIDER: buttondown
+      PLAYWRIGHT_BROWSERS_PATH: /opt/playwright-tools/browsers
     depends_on:
       db:
         condition: service_healthy