Add category taxonomy and navigation integration

Implements Issue #35 with category snippets, article category routing, category-aware templates, and category RSS feeds with tests.

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

apps/blog/migrations/0002_category_articlepage_category.py

@@ -0,0 +1,86 @@
+# Generated by Django 5.2.11 on 2026-03-03
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+def create_default_category(apps, schema_editor):
+    Category = apps.get_model("blog", "Category")
+    Category.objects.get_or_create(
+        slug="general",
+        defaults={
+            "name": "General",
+            "description": "General articles",
+            "colour": "neutral",
+            "sort_order": 0,
+            "show_in_nav": True,
+        },
+    )
+
+
+def assign_default_category_to_articles(apps, schema_editor):
+    Category = apps.get_model("blog", "Category")
+    ArticlePage = apps.get_model("blog", "ArticlePage")
+    default_category = Category.objects.get(slug="general")
+    ArticlePage.objects.filter(category__isnull=True).update(category=default_category)
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("blog", "0001_initial"),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="Category",
+            fields=[
+                ("id", models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name="ID")),
+                ("name", models.CharField(max_length=100, unique=True)),
+                ("slug", models.SlugField(unique=True)),
+                ("description", models.TextField(blank=True)),
+                (
+                    "hero_image",
+                    models.ForeignKey(
+                        blank=True,
+                        null=True,
+                        on_delete=django.db.models.deletion.SET_NULL,
+                        related_name="+",
+                        to="wagtailimages.image",
+                    ),
+                ),
+                (
+                    "colour",
+                    models.CharField(
+                        choices=[("cyan", "Cyan"), ("pink", "Pink"), ("neutral", "Neutral")],
+                        default="neutral",
+                        max_length=20,
+                    ),
+                ),
+                ("sort_order", models.IntegerField(default=0)),
+                ("show_in_nav", models.BooleanField(default=True)),
+            ],
+            options={"ordering": ["sort_order", "name"]},
+        ),
+        migrations.AddField(
+            model_name="articlepage",
+            name="category",
+            field=models.ForeignKey(
+                blank=True,
+                null=True,
+                on_delete=django.db.models.deletion.PROTECT,
+                related_name="articles",
+                to="blog.category",
+            ),
+        ),
+        migrations.RunPython(create_default_category, migrations.RunPython.noop),
+        migrations.RunPython(assign_default_category_to_articles, migrations.RunPython.noop),
+        migrations.AlterField(
+            model_name="articlepage",
+            name="category",
+            field=models.ForeignKey(
+                on_delete=django.db.models.deletion.PROTECT,
+                related_name="articles",
+                to="blog.category",
+            ),
+        ),
+    ]