feat(centralui): Templates tree context menu — "New Instance…" (Deployer-gated)

Claude-Session: https://claude.ai/code/session_01G2GHPnbbKGvyyfbr2XBRVH

src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Design/Templates.razor

@@ -130,10 +130,16 @@
     private bool _loading = true;
     private string? _errorMessage;
 
+    // "New Instance…" leaves the Design area for a RequireDeployment page; only offer
+    // it to users who hold that role so the menu never leads to a 403.
+    private bool _canCreateInstances;
+
     private ToastNotification _toast = default!;
 
     protected override async Task OnInitializedAsync()
     {
+        var state = await AuthStateProvider.GetAuthenticationStateAsync();
+        _canCreateInstances = state.User.HasClaim(JwtTokenService.RoleClaimType, Roles.Deployer);
         await LoadTemplatesAsync();
     }
 
@@ -302,6 +308,13 @@
                 {
                     <button class="dropdown-item" @onclick="() => OpenComposeDialog(tmpl)">Compose into…</button>
                 }
+                @if (_canCreateInstances)
+                {
+                    <div class="dropdown-divider"></div>
+                    <button class="dropdown-item" data-test="ctx-new-instance"
+                            @onclick='() => NavigationManager.NavigateTo($"/deployment/instances/create?templateId={node.Id}")'>New Instance…</button>
+                    <div class="dropdown-divider"></div>
+                }
                 <button class="dropdown-item" @onclick="() => OpenMoveTemplateDialog(node.Id, node.Name)">Move to Folder…</button>
                 <div class="dropdown-divider"></div>
                 @if (tmpl != null)