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/templates/navbar.html

@@ -44,6 +44,11 @@
                     <li class="nav-item">
                         <a class="nav-link {% if request.resolver_match.namespace == 'customers' %}active{% endif %}" href="{% url 'customers:customer-list' %}">Клиенты</a>
                     </li>
+                    {% if request.user.is_owner or request.user.is_superuser %}
+                    <li class="nav-item">
+                        <a class="nav-link {% if request.resolver_match.namespace == 'user_roles' %}active{% endif %}" href="{% url 'user_roles:list' %}">Роли</a>
+                    </li>
+                    {% endif %}
                     <li class="nav-item">
                         <a class="nav-link {% if request.resolver_match.namespace == 'pos' %}active{% endif %}" href="{% url 'pos:terminal' %}">Касса</a>
                     </li>