Implement Role Management Features and UI Enhancements

- Introduced a new composable `useActiveRole` for managing user roles, including fetching role status and switching roles with server validation.
- Updated `RoleSwitcher.vue` to utilize the new composable, enhancing role selection with improved error handling and UI feedback.
- Added new API endpoints for role management, including fetching user role status and switching active roles.
- Enhanced product visibility logic to filter based on the user's active role, ensuring a tailored experience.
- Updated database schema to support last active role tracking for users, improving session management.
- Refined UI components across the application to reflect role-based changes and improve user experience.

server/database/schema.ts

@@ -127,6 +127,9 @@ export const users = pgTable('users', {
   city: text('city'),
   countryCode: text('country_code'), // ISO 3166-1 alpha-2 (e.g., 'DE', 'AT')
 
+  // Role preference (last selected role, used as default after login)
+  lastActiveRoleCode: roleCodeEnum('last_active_role_code'),
+
   createdAt: timestamp('created_at').defaultNow().notNull(),
   updatedAt: timestamp('updated_at').defaultNow().notNull(),
 })