Refactor API clients to use interface-based DI

Introduce interfaces for all API clients and update dependency injection to use these interfaces. Refactor services and components to depend on abstractions instead of concrete implementations, improving testability and maintainability.

DbFirst.BlazorWebApp/Services/BandLayoutService.cs

@@ -5,7 +5,7 @@ using System.Text.Json;
 
 namespace DbFirst.BlazorWebApp.Services
 {
-    public class BandLayoutService(LayoutApiClient layoutApi, IJSRuntime jsRuntime)
+    public class BandLayoutService(ILayoutApiClient layoutApi, IJSRuntime jsRuntime)
     {
         private const string LayoutUserStorageKey = "layoutUser";
         private readonly JsonSerializerOptions _jsonOptions = new(JsonSerializerDefaults.Web);