feat: implement article search with PostgreSQL full-text search

- Configure Wagtail database search backend with English search config
- Add django.contrib.postgres to INSTALLED_APPS for full PG FTS support
- Expand ArticlePage.search_fields: body_text (excl. code blocks),
  AutocompleteField(title), RelatedFields(tags), FilterFields
- Add search view at /search/?q= with query guards (strip, max 200 chars,
  empty/whitespace handling) and pagination preserving query param
- Replace nav Subscribe CTA with compact search box (desktop + mobile)
- Add search box to article index page alongside category/tag filters
- Create search results template reusing article_card component
- Add update_index to deploy entrypoint for automated reindexing
- Update existing tests for nav change, add comprehensive search tests

Closes #41

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

apps/blog/tests/test_search.py

@@ -0,0 +1,140 @@
+import pytest
+
+from apps.blog.models import ArticleIndexPage, ArticlePage
+from apps.blog.tests.factories import AuthorFactory
+from apps.blog.views import MAX_QUERY_LENGTH
+
+
+@pytest.fixture
+def search_articles(home_page):
+    """Create an article index with searchable articles."""
+    index = ArticleIndexPage(title="Articles", slug="articles")
+    home_page.add_child(instance=index)
+    author = AuthorFactory()
+    articles = []
+    for title, summary in [
+        ("Understanding LLM Benchmarks", "A deep dive into how language models are evaluated"),
+        ("Local Models on Apple Silicon", "Running open-source models on your MacBook"),
+        ("Agent Frameworks Compared", "Comparing LangChain, CrewAI, and AutoGen"),
+    ]:
+        a = ArticlePage(
+            title=title,
+            slug=title.lower().replace(" ", "-"),
+            author=author,
+            summary=summary,
+            body=[("rich_text", f"<p>{summary} in detail.</p>")],
+        )
+        index.add_child(instance=a)
+        a.save_revision().publish()
+        articles.append(a)
+    return articles
+
+
+@pytest.mark.django_db
+class TestSearchView:
+    def test_empty_query_returns_no_results(self, client, home_page):
+        resp = client.get("/search/")
+        assert resp.status_code == 200
+        assert resp.context["query"] == ""
+        assert resp.context["results"] is None
+
+    def test_whitespace_query_returns_no_results(self, client, home_page):
+        resp = client.get("/search/?q=   ")
+        assert resp.status_code == 200
+        assert resp.context["query"] == ""
+        assert resp.context["results"] is None
+
+    def test_search_returns_matching_articles(self, client, search_articles):
+        resp = client.get("/search/?q=benchmarks")
+        assert resp.status_code == 200
+        assert resp.context["query"] == "benchmarks"
+        assert resp.context["results"] is not None
+
+    def test_search_no_match_returns_empty_page(self, client, search_articles):
+        resp = client.get("/search/?q=zzzznonexistent")
+        assert resp.status_code == 200
+        assert resp.context["query"] == "zzzznonexistent"
+        # Either None or empty page object
+        results = resp.context["results"]
+        if results is not None:
+            assert len(list(results)) == 0
+
+    def test_query_is_truncated_to_max_length(self, client, home_page):
+        long_query = "a" * 500
+        resp = client.get(f"/search/?q={long_query}")
+        assert resp.status_code == 200
+        assert len(resp.context["query"]) <= MAX_QUERY_LENGTH
+
+    def test_query_preserved_in_template(self, client, search_articles):
+        resp = client.get("/search/?q=LLM")
+        html = resp.content.decode()
+        assert 'value="LLM"' in html
+
+    def test_search_results_page_renders(self, client, search_articles):
+        resp = client.get("/search/?q=models")
+        assert resp.status_code == 200
+        html = resp.content.decode()
+        assert "Search" in html
+
+    def test_search_url_resolves(self, client, home_page):
+        from django.urls import reverse
+        assert reverse("search") == "/search/"
+
+
+@pytest.mark.django_db
+class TestSearchFields:
+    def test_search_fields_include_summary(self):
+        field_names = [
+            f.field_name for f in ArticlePage.search_fields if hasattr(f, "field_name")
+        ]
+        assert "summary" in field_names
+
+    def test_search_fields_include_body_text(self):
+        field_names = [
+            f.field_name for f in ArticlePage.search_fields if hasattr(f, "field_name")
+        ]
+        assert "body_text" in field_names
+
+    def test_search_fields_include_autocomplete_title(self):
+        from wagtail.search.index import AutocompleteField
+        autocomplete_fields = [
+            f for f in ArticlePage.search_fields if isinstance(f, AutocompleteField)
+        ]
+        assert any(f.field_name == "title" for f in autocomplete_fields)
+
+    def test_search_fields_include_related_tags(self):
+        from wagtail.search.index import RelatedFields
+        related = [f for f in ArticlePage.search_fields if isinstance(f, RelatedFields)]
+        assert any(f.field_name == "tags" for f in related)
+
+    def test_body_text_excludes_code_blocks(self):
+        author = AuthorFactory()
+        article = ArticlePage(
+            title="Test",
+            slug="test",
+            author=author,
+            summary="summary",
+            body=[
+                ("rich_text", "<p>prose content here</p>"),
+                ("code", {"language": "python", "filename": "", "raw_code": "def secret(): pass"}),
+            ],
+        )
+        assert "prose content here" in article.body_text
+        assert "secret" not in article.body_text
+
+
+@pytest.mark.django_db
+class TestSearchNavIntegration:
+    def test_nav_contains_search_form(self, client, home_page):
+        resp = client.get("/")
+        html = resp.content.decode()
+        assert 'role="search"' in html
+        assert 'name="q"' in html
+        assert 'placeholder="Search articles..."' in html
+
+    def test_article_index_contains_search_form(self, client, home_page):
+        index = ArticleIndexPage(title="Articles", slug="articles")
+        home_page.add_child(instance=index)
+        resp = client.get("/articles/")
+        html = resp.content.decode()
+        assert 'name="q"' in html

apps/blog/tests/test_views.py

@@ -69,8 +69,9 @@ def test_newsletter_forms_render_in_nav_and_footer(client, home_page):
     resp = client.get("/")
     html = resp.content.decode()
     assert resp.status_code == 200
-    # Nav has a Subscribe CTA link (no inline form — wireframe spec)
-    assert 'href="#newsletter"' in html
+    # Nav has a search form instead of Subscribe CTA
+    assert 'role="search"' in html
+    assert 'name="q"' in html
     # Footer has Connect section with social/RSS links (no newsletter form)
     assert "Connect" in html
     assert 'name="source" value="nav"' not in html