fix: restore Encore-based asset wiring, drop stranded AssetMapper calls

The AssetMapper migration moved to PR #81 but the dashboard and base
template still referenced AssetMapper, causing every admin smoke test
to 500 with "AssetMapper component is not installed".

- DashboardController::configureAssets() goes back to addCssFile('css/admin.css')
- base.html.twig drops the {{ importmap('app') }} block

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: turegjorup

src/Controller/Admin/DashboardController.php

@@ -81,6 +81,6 @@ public function configureCrud(): Crud
     #[\Override]
     public function configureAssets(): Assets
     {
-        return parent::configureAssets()->addAssetMapperEntry('app');
+        return Assets::new()->addCssFile('css/admin.css');
     }
 }

templates/base.html.twig

@@ -10,7 +10,6 @@
         {% endblock %}
 
         {% block javascripts %}
-            {% block importmap %}{{ importmap('app') }}{% endblock %}
             {{ encore_entry_script_tags('app') }}
         {% endblock %}
     </head>