feat: add solutions app, fix HomePage subpage_types, add pytest test suite

- apps/solutions: SolutionIndexPage/SolutionPage (mirrors products/cases)
- apps/home: HomePage.subpage_types now includes products/solutions/cases index pages (previously only blog, blocking admin page creation)
- pytest.ini + conftest.py (root_page/home_page fixtures)
- unit tests for core (SEOablePage, FormBlock API repr), products, cases, forms (lead submit API)

apps/products/tests.py

@@ -0,0 +1,34 @@
+"""apps.products 单元测试：页面树结构与列表上下文。"""
+import pytest
+
+from apps.products.models import ProductIndexPage, ProductPage
+
+pytestmark = pytest.mark.django_db
+
+
+@pytest.fixture
+def product_index(home_page):
+    index = ProductIndexPage(title="产品", slug="products", intro="我们的产品")
+    home_page.add_child(instance=index)
+    return index
+
+
+def test_product_page_can_be_created_under_index(product_index):
+    product = ProductPage(title="产品 A", slug="product-a", summary="简介 A")
+    product_index.add_child(instance=product)
+
+    assert ProductPage.objects.live().descendant_of(product_index).count() == 1
+
+
+def test_product_index_context_lists_live_products_only(product_index):
+    live_product = ProductPage(title="产品 A", slug="product-a")
+    product_index.add_child(instance=live_product)
+
+    draft_product = ProductPage(title="产品 B", slug="product-b", live=False)
+    product_index.add_child(instance=draft_product)
+
+    context = product_index.get_context(request=None)
+    titles = [p.title for p in context["products"]]
+
+    assert "产品 A" in titles
+    assert "产品 B" not in titles