feat(ui/topology): open instance in Debug View from context menu

Adds a Debug View item to the instance context menu on /deployment/topology
that navigates to /deployment/debug-view with siteId and instanceId query
parameters; the page now auto-connects when those are present (falling
back to the existing localStorage auto-reconnect otherwise). Disabled for
non-Enabled instances since debug streaming only targets enabled ones.

Also fixes a latent NRE in DebugView.OnInitializedAsync: the toast ref
isn't bound yet during init, so transient load failures are now stashed
and surfaced from OnAfterRenderAsync where the toast is ready.

src/ScadaLink.CentralUI/Components/Pages/Deployment/DebugView.razor

@@ -247,6 +247,9 @@
 @code {
     private const int MaxRows = 200;
 
+    [SupplyParameterFromQuery] public int? SiteId { get; set; }
+    [SupplyParameterFromQuery] public int? InstanceId { get; set; }
+
     private List<Site> _sites = new();
     private List<Instance> _siteInstances = new();
     private int _selectedSiteId;
@@ -287,6 +290,8 @@
     private DebugStreamSession? _session;
     private ToastNotification _toast = default!;
 
+    private string? _initError;
+
     protected override async Task OnInitializedAsync()
     {
         try
@@ -295,7 +300,7 @@
         }
         catch (Exception ex)
         {
-            _toast.ShowError($"Failed to load sites: {ex.Message}");
+            _initError = $"Failed to load sites: {ex.Message}";
         }
         _loading = false;
     }
@@ -304,6 +309,29 @@
     {
         if (!firstRender) return;
 
+        if (_initError != null)
+        {
+            _toast.ShowError(_initError);
+            _initError = null;
+        }
+
+        if (SiteId is > 0 && InstanceId is > 0)
+        {
+            _selectedSiteId = SiteId.Value;
+            await LoadInstancesForSite();
+            if (_siteInstances.Any(i => i.Id == InstanceId.Value))
+            {
+                _selectedInstanceId = InstanceId.Value;
+                await Connect();
+            }
+            else
+            {
+                _toast.ShowError("Requested instance is not available for debug streaming.");
+            }
+            StateHasChanged();
+            return;
+        }
+
         var storedSiteId = await JS.InvokeAsync<string>("localStorage.getItem", "debugView.siteId");
         var storedInstanceId = await JS.InvokeAsync<string>("localStorage.getItem", "debugView.instanceId");
 

src/ScadaLink.CentralUI/Components/Pages/Deployment/Topology.razor

@@ -452,6 +452,11 @@
                         @onclick='() => NavigationManager.NavigateTo($"/deployment/instances/{inst.Id}/configure")'>
                     Configure
                 </button>
+                <button class="dropdown-item"
+                        @onclick='() => NavigationManager.NavigateTo($"/deployment/debug-view?siteId={node.SiteId}&instanceId={inst.Id}")'
+                        disabled="@(inst.State != InstanceState.Enabled)">
+                    Debug View
+                </button>
                 <button class="dropdown-item" @onclick="() => ShowDiff(inst)"
                         disabled="@(_actionInProgress || inst.State == InstanceState.NotDeployed)">Diff</button>
                 <button class="dropdown-item" @onclick="() => OpenMoveInstanceDialog(node)">Move to Area…</button>