feat(ui/templates): derived-template action and slimmer composition row

Right-click a template now offers "New Derived Template" — opens
TemplateCreate with the parent pre-selected via a new ?parentId query
parameter. Composition rows in the tree drop the trailing
"→ TargetName" muted text; the kind glyph plus the instance name carry
enough meaning, and the composed template is one click away from the
row's right-click menu.

src/ScadaLink.CentralUI/Components/Pages/Design/Templates.razor

@@ -239,13 +239,8 @@
                 break;
 
             case TmplNodeKind.Composition:
-                var composedName = _templates.FirstOrDefault(t => t.Id == node.Composition!.ComposedTemplateId)?.Name
-                                   ?? $"#{node.Composition!.ComposedTemplateId}";
                 <span class="tv-glyph"><i class="bi bi-arrow-return-right"></i></span>
-                <span class="tv-label" title="@node.Label">
-                    @node.Label
-                    <span class="text-muted small ms-1">→ @composedName</span>
-                </span>
+                <span class="tv-label" title="@node.Label">@node.Label</span>
                 break;
         }
     };
@@ -282,6 +277,7 @@
                 break;
 
             case TmplNodeKind.Template:
+                <button class="dropdown-item" @onclick='() => NavigationManager.NavigateTo($"/design/templates/create?parentId={node.EntityId}")'>New Derived Template</button>
                 <button class="dropdown-item" @onclick="() => OpenMoveTemplateDialog(node.EntityId, node.Label)">Move to Folder…</button>
                 <div class="dropdown-divider"></div>
                 <button class="dropdown-item text-danger" @onclick="() => DeleteTemplate(node.Template!)">Delete</button>