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)

conftest.py

@@ -0,0 +1,19 @@
+import pytest
+
+
+@pytest.fixture
+def root_page():
+    """Wagtail 初始迁移创建的树根页面（depth=1）。"""
+    from wagtail.models import Page
+
+    return Page.objects.get(depth=1)
+
+
+@pytest.fixture
+def home_page(root_page):
+    """在树根下创建一个测试用 HomePage 实例。"""
+    from apps.home.models import HomePage
+
+    page = HomePage(title="首页", slug="home-test")
+    root_page.add_child(instance=page)
+    return page