Update dashboard navigation and dynamic loading

- Changed NavMenu to link to /dashboards instead of /dashboards/default
- Refactored Dashboard.razor to list dashboards from API
- Dashboard viewer/designer now loads by selected dashboard ID
- Mode toggle preserves selected dashboard and mode
- Added DashboardApiClient and DashboardInfoDto for API integration
- Registered DashboardApiClient for DI and HTTP client setup in Program.cs

DbFirst.BlazorWebApp/Program.cs

@@ -17,10 +17,15 @@ if (!string.IsNullOrWhiteSpace(apiBaseUrl))
     {
         client.BaseAddress = new Uri(apiBaseUrl);
     });
+    builder.Services.AddHttpClient<DashboardApiClient>(client =>
+    {
+        client.BaseAddress = new Uri(apiBaseUrl);
+    });
 }
 else
 {
     builder.Services.AddHttpClient<CatalogApiClient>();
+    builder.Services.AddHttpClient<DashboardApiClient>();
 }
 
 var app = builder.Build();