Set WebRootPath, enable static file serving, and upgrade to .NET 9.0

API/Program.cs

@@ -2,7 +2,13 @@ using API.Database;
 using API.Repository.AgeGroup;
 using Microsoft.EntityFrameworkCore;
 
-var builder = WebApplication.CreateBuilder(args);
+var webRoot = Path.GetFullPath(Path.Combine(Directory.GetCurrentDirectory(), "..", "wwwroot"));
+
+var builder = WebApplication.CreateBuilder(new WebApplicationOptions
+{
+    Args = args,
+    WebRootPath = webRoot
+});
 
 builder.Services.AddControllers();
 builder.Services.AddEndpointsApiExplorer();
@@ -43,10 +49,16 @@ using(var scope = app.Services.CreateScope())
     dbContext.Database.Migrate();
 }
 
+// Deliver frontend
+app.UseDefaultFiles();
+app.UseStaticFiles();
+
 app.UseHttpsRedirection();
 
 app.UseAuthorization();
 
 app.MapControllers();
+// Frontend Fallback
+app.MapFallbackToFile("index.html");
 
 app.Run();