refactor(wbs-ux): route root authenticated users to Vue templates and map SPA fallback

src/dotnet/QuantEngine.Web/Program.cs

@@ -192,11 +192,11 @@ try
         Log.Warning("Hangfire setup failed: {Message}", ex.Message);
     }
 
-    // Root redirect: unauthenticated → /Account/Login, authenticated → /Admin/Dashboard
+    // Root redirect: unauthenticated → /Account/Login, authenticated → Vue 3 SPA /templates
     app.MapGet("/", context =>
     {
         if (context.User?.Identity?.IsAuthenticated ?? false)
-            context.Response.Redirect("/Admin/Dashboard");
+            context.Response.Redirect("/templates");
         else
             context.Response.Redirect("/Account/Login");
         return Task.CompletedTask;
@@ -210,6 +210,8 @@ try
     });
 
     app.MapRazorPages();
+    app.MapFallbackToFile("index.html");
+
 
     app.Run();
 }