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/solutions/apps.py

@@ -0,0 +1,8 @@
+from django.apps import AppConfig
+
+
+class SolutionsConfig(AppConfig):
+    default_auto_field = "django.db.models.BigAutoField"
+    name = "apps.solutions"
+    label = "solutions"
+    verbose_name = "解决方案"