Refactor API base URL config to use AppSettings class

Replaced direct IConfiguration usage with a strongly-typed AppSettings class for accessing the API base URL. Registered AppSettings with DI and updated Dashboard.razor to use IOptions<AppSettings>. Updated using statements and DI setup for improved type safety and centralized configuration management.

DbFirst.BlazorWebApp/AppSettings.cs

@@ -0,0 +1,6 @@
+namespace DbFirst.BlazorWebApp;
+
+public class AppSettings
+{
+    public string ApiBaseUrl { get; set; } = string.Empty;
+}