feat: implement multi-tenant member management and UI improvements

- Add multi-tenant support (isAddTenant, isRemoveTenant) to backend UpdateUser API.
- Update UserRepository to support searching in company_codes array.
- Implement table sorting and align search bar layout in adminfront.
- Add 'Assign Existing Member' and 'Exclude from Organization' features to TenantUsersPage.
- Auto-populate tenantSlug in UserCreatePage via query parameters.
- Add necessary localization keys for new UI elements.

Resolves #644, #639, #642, #641

adminfront/src/lib/adminApi.ts

@@ -433,6 +433,8 @@ export type UserUpdateRequest = {
   role?: string;
   status?: string;
   tenantSlug?: string;
+  isAddTenant?: boolean;
+  isRemoveTenant?: boolean;
   department?: string;
   position?: string;
   jobTitle?: string;