feat: add user roles management UI with owner access control

- Added role management views (list, create, edit, delete)
- Created user_roles URL routing
- Added role management templates with Bootstrap styling
- Updated navbar with Roles link for owners and superusers
- Enhanced decorators and mixins with superuser bypass
- Added assign_owner_role.py utility script

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

myproject/user_roles/urls.py

@@ -0,0 +1,11 @@
+from django.urls import path
+from . import views
+
+app_name = 'user_roles'
+
+urlpatterns = [
+    path('', views.user_role_list, name='list'),
+    path('create/', views.user_role_create, name='create'),
+    path('<int:pk>/edit/', views.user_role_edit, name='edit'),
+    path('<int:pk>/delete/', views.user_role_delete, name='delete'),
+]