Fix Django migration issues and add missing URLs

- Create missing templates app urls.py
- Fix REST_FRAMEWORK pagination settings
- Add DEFAULT_AUTO_FIELD configuration
- Create migration files for all apps
- Fix auto-generated model warnings
- Verify database setup with test project

backend/apps/templates/urls.py

@@ -0,0 +1,9 @@
+from django.urls import path
+from .views import template_list, template_detail
+
+app_name = 'templates'
+
+urlpatterns = [
+    path('templates/', template_list, name='template-list'),
+    path('templates/<str:pk>/', template_detail, name='template-detail'),
+]