feat: add comprehensive Playwright E2E test suite

- Create e2e/ directory with 7 test modules covering:
  - Home page: title, nav links, theme toggle, newsletter form
  - Cookie consent: accept all, reject all, granular prefs, persistence
  - Article index: loads, tag filter, click-through navigation
  - Article detail: title/read-time, share section, comments, newsletter aside, related
  - Comments: valid submit → redirect, empty body → error display, disabled check
  - Newsletter: JS confirmation message, invalid email error, aside form, duplicate
  - Feeds: RSS/sitemap/robots.txt validity, tag feed, seeded content present
- Extend seed_e2e_content management command with tagged article, about page,
  no-comments article, and legal pages for richer test coverage
- Add seed command tests (create + idempotency) to keep coverage ≥ 90%
- Add pr-e2e CI job (runs on pull_request): builds image, starts postgres + app,
  installs playwright, runs pytest e2e/
- Update nightly-e2e to run full e2e/ suite alongside legacy journey test
- Add --ignore=e2e to unit-test pytest step (coverage must not include browser tests)

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

e2e/test_newsletter.py

@@ -0,0 +1,62 @@
+"""E2E tests for the newsletter subscription form."""
+
+from __future__ import annotations
+
+import pytest
+from playwright.sync_api import Page, expect
+
+
+def _nav_newsletter_form(page: Page):
+    return page.locator("nav").locator("form[data-newsletter-form]")
+
+
+@pytest.mark.e2e
+def test_subscribe_valid_email_shows_confirmation(page: Page, base_url: str) -> None:
+    page.goto(f"{base_url}/", wait_until="networkidle")
+    form = _nav_newsletter_form(page)
+    form.locator('input[type="email"]').fill("playwright-test@example.com")
+    form.get_by_role("button", name="Subscribe").click()
+
+    # JS sets the data-newsletter-message text on success
+    message = form.locator("[data-newsletter-message]")
+    expect(message).to_have_text("Check your email to confirm your subscription.", timeout=5_000)
+
+
+@pytest.mark.e2e
+def test_subscribe_invalid_email_shows_error(page: Page, base_url: str) -> None:
+    page.goto(f"{base_url}/", wait_until="networkidle")
+    form = _nav_newsletter_form(page)
+    form.locator('input[type="email"]').fill("not-an-email")
+    form.get_by_role("button", name="Subscribe").click()
+
+    message = form.locator("[data-newsletter-message]")
+    expect(message).to_have_text("Please enter a valid email.", timeout=5_000)
+
+
+@pytest.mark.e2e
+def test_subscribe_from_article_aside(page: Page, base_url: str) -> None:
+    """Newsletter form embedded in the article aside also works."""
+    page.goto(f"{base_url}/articles/nightly-playwright-journey/", wait_until="networkidle")
+    aside_form = page.locator("aside").locator("form[data-newsletter-form]")
+    aside_form.locator('input[type="email"]').fill("aside-test@example.com")
+    aside_form.get_by_role("button", name="Subscribe").click()
+
+    message = aside_form.locator("[data-newsletter-message]")
+    expect(message).to_have_text("Check your email to confirm your subscription.", timeout=5_000)
+
+
+@pytest.mark.e2e
+def test_subscribe_duplicate_email_still_shows_confirmation(page: Page, base_url: str) -> None:
+    """Submitting the same address twice must not expose an error to the user."""
+    email = "dupe-e2e@example.com"
+    page.goto(f"{base_url}/", wait_until="networkidle")
+    form = _nav_newsletter_form(page)
+    form.locator('input[type="email"]').fill(email)
+    form.get_by_role("button", name="Subscribe").click()
+    message = form.locator("[data-newsletter-message]")
+    expect(message).to_have_text("Check your email to confirm your subscription.", timeout=5_000)
+
+    # Second submission — form resets after first, so fill again
+    form.locator('input[type="email"]').fill(email)
+    form.get_by_role("button", name="Subscribe").click()
+    expect(message).to_have_text("Check your email to confirm your subscription.", timeout=5_000)