Initial Blazor Web App template

Rider-generated Blazor Web App (net10.0, interactive render mode None,
no auth scaffold, no sample pages). Includes Rider auto-formatting.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Elternbeirat.Web/Components/Routes.razor

@@ -0,0 +1,6 @@
+<Router AppAssembly="typeof(Program).Assembly" NotFoundPage="typeof(Pages.NotFound)">
+    <Found Context="routeData">
+        <RouteView RouteData="routeData" DefaultLayout="typeof(Layout.MainLayout)"/>
+        <FocusOnNavigate RouteData="routeData" Selector="h1"/>
+    </Found>
+</Router>