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.BlazorWasm/Services/DashboardApiClient.cs

@@ -0,0 +1,21 @@
+using System.Net.Http.Json;
+using DbFirst.BlazorWasm.Models;
+
+namespace DbFirst.BlazorWasm.Services;
+
+public class DashboardApiClient
+{
+    private readonly HttpClient _httpClient;
+    private const string Endpoint = "api/dashboard/dashboards";
+
+    public DashboardApiClient(HttpClient httpClient)
+    {
+        _httpClient = httpClient;
+    }
+
+    public async Task<List<DashboardInfoDto>> GetAllAsync()
+    {
+        var result = await _httpClient.GetFromJsonAsync<List<DashboardInfoDto>>(Endpoint);
+        return result ?? new List<DashboardInfoDto>();
+    }
+}