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/views.py

@@ -0,0 +1,43 @@
+from __future__ import annotations
+
+from django.core.paginator import EmptyPage, PageNotAnInteger, Paginator
+from django.http import HttpRequest, HttpResponse
+from django.template.response import TemplateResponse
+
+from apps.blog.models import ArticlePage
+
+RESULTS_PER_PAGE = 12
+MAX_QUERY_LENGTH = 200
+
+
+def search(request: HttpRequest) -> HttpResponse:
+    query = request.GET.get("q", "").strip()[:MAX_QUERY_LENGTH]
+    results_page = None
+    paginator = None
+
+    if query:
+        results = (
+            ArticlePage.objects.live()
+            .public()
+            .select_related("author", "category")
+            .prefetch_related("tags__metadata")
+            .search(query)
+        )
+        paginator = Paginator(results, RESULTS_PER_PAGE)
+        page_num = request.GET.get("page")
+        try:
+            results_page = paginator.page(page_num)
+        except PageNotAnInteger:
+            results_page = paginator.page(1)
+        except EmptyPage:
+            results_page = paginator.page(paginator.num_pages)
+
+    return TemplateResponse(
+        request,
+        "blog/search_results.html",
+        {
+            "query": query,
+            "results": results_page,
+            "paginator": paginator,
+        },
+    )