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/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>