Add real-time dashboard updates with SignalR

Integrate SignalR to provide real-time dashboard update notifications.
- Added DashboardsHub and DashboardChangeNotifier on the backend.
- Modified SqlDashboardStorage to trigger notifications on changes.
- Registered SignalR services and mapped the hub endpoint.
- Updated Blazor clients to connect to the hub and refresh dashboards on change.
- Added SignalR client packages and necessary DI/configuration.

DbFirst.BlazorWebApp/Components/Pages/Dashboard.razor

@@ -1,5 +1,6 @@
 @page "/dashboard"
 @page "/dashboards/{DashboardId?}"
+@implements IAsyncDisposable
 @inject Microsoft.Extensions.Configuration.IConfiguration Configuration
 @inject NavigationManager Navigation
 @inject DashboardApiClient DashboardApi
@@ -77,19 +78,38 @@
     [SupplyParameterFromQuery] public string? Mode { get; set; }
 
     private readonly List<DashboardInfoDto> dashboards = new();
+    private HubConnection? _hubConnection;
 
     private bool IsDesigner => !string.Equals(Mode, "viewer", StringComparison.OrdinalIgnoreCase);
     private WorkingMode CurrentMode => IsDesigner ? WorkingMode.Designer : WorkingMode.ViewerOnly;
-    private string SelectedDashboardId { get; set; } = "";
+    private string SelectedDashboardId { get; set; } = string.Empty;
     private string DashboardKey => $"{SelectedDashboardId}-{(IsDesigner ? "designer" : "viewer")}";
 
     private string DashboardEndpoint => $"{Configuration["ApiBaseUrl"]?.TrimEnd('/')}/api/dashboard";
+    private string HubEndpoint => $"{Configuration["ApiBaseUrl"]?.TrimEnd('/')}/hubs/dashboards";
+
+    protected override async Task OnInitializedAsync()
+    {
+        await RefreshDashboards();
+
+        _hubConnection = new HubConnectionBuilder()
+            .WithUrl(HubEndpoint)
+            .WithAutomaticReconnect()
+            .Build();
+
+        _hubConnection.On("DashboardsChanged", async () =>
+        {
+            await RefreshDashboards();
+        });
+
+        await _hubConnection.StartAsync();
+    }
 
     protected override async Task OnParametersSetAsync()
     {
         if (dashboards.Count == 0)
         {
-            dashboards.AddRange(await DashboardApi.GetAllAsync());
+            await RefreshDashboards();
         }
 
         var requestedId = string.IsNullOrWhiteSpace(DashboardId) || string.Equals(DashboardId, "default", StringComparison.OrdinalIgnoreCase)
@@ -119,4 +139,25 @@
         var targetMode = IsDesigner ? "viewer" : "designer";
         Navigation.NavigateTo($"dashboards/{SelectedDashboardId}?mode={targetMode}", replace: true);
     }
+
+    private async Task RefreshDashboards()
+    {
+        var latest = await DashboardApi.GetAllAsync();
+        if (latest.Count == dashboards.Count && latest.All(d => dashboards.Any(x => x.Id == d.Id && x.Name == d.Name)))
+        {
+            return;
+        }
+
+        dashboards.Clear();
+        dashboards.AddRange(latest);
+        await InvokeAsync(StateHasChanged);
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        if (_hubConnection != null)
+        {
+            await _hubConnection.DisposeAsync();
+        }
+    }
 }

DbFirst.BlazorWebApp/Components/_Imports.razor

@@ -6,6 +6,7 @@
 @using static Microsoft.AspNetCore.Components.Web.RenderMode
 @using Microsoft.AspNetCore.Components.Web.Virtualization
 @using Microsoft.JSInterop
+@using Microsoft.AspNetCore.SignalR.Client
 @using DbFirst.BlazorWebApp
 @using DbFirst.BlazorWebApp.Components
 @using DbFirst.BlazorWebApp.Models

DbFirst.BlazorWebApp/DbFirst.BlazorWebApp.csproj

@@ -12,5 +12,9 @@
     <PackageReference Include="DevExpress.Blazor.Themes" Version="25.2.3" />
     <PackageReference Include="DevExpress.Blazor.Themes.Fluent" Version="25.2.3" />
   </ItemGroup>
+  <ItemGroup>
+    <PackageReference Include="DevExpress.Blazor" Version="25.2.3" />
+    <PackageReference Include="Microsoft.AspNetCore.SignalR.Client" Version="8.0.22" />
+  </ItemGroup>
 
 </Project>