Follow-ups: reference reorder, detach service_id, named-dashboard widgets

Three reusable-widget follow-up fixes:

1. Reference sort_order independently reorderable. Reordering a
   referenced widget now updates the widget_references.sort_order (per-
   dashboard), not the shared widget instance sort_order. New backend
   update_widget_reference method + PUT /api/widgets/references/{id}
   endpoint. Frontend moveInstance checks _ref_id to choose the right
   mutation (updateRef for references, saveWidget for owned).

2. Detach preserves service_id. detach_widget_reference now copies the
   original widget's service_id into the clone, so service-bound widgets
   (Grafana chart, Jellyfin activity) continue to render after detach.

3. Named dashboards support widget references. NamedDashboardPage
   fetches useWidgetReferences('named:<slug>') and renders them via
   WidgetInstanceCard alongside pinned links. 'Edit widgets' button
   opens WidgetConfigDialog with dashboardScope='named:<slug>'.

Also: removed useMemo on combinedWidgets in WidgetConfigDialog to fix
a react-hooks/preserve-manual-memoization lint error (the React Compiler
ESLint plugin couldn't verify the spread+sort memoization).

283 backend tests pass (+1 update_reference test); 128 frontend tests
pass; ruff clean; 0 lint errors.

frontend/src/pages/__tests__/NamedDashboardPage.test.tsx

@@ -1,21 +1,39 @@
 import { describe, it, expect, vi, beforeEach } from "vitest";
 import { render, screen } from "@testing-library/react";
 import { MemoryRouter, Route, Routes } from "react-router-dom";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
 import { NamedDashboardPage } from "../NamedDashboardPage";
 
 vi.mock("../../hooks/useDashboards", () => ({
 	useDashboardBySlug: vi.fn(() => ({ data: undefined, isLoading: true })),
 }));
 
+vi.mock("../../hooks/useWidgets", () => ({
+	useWidgetReferences: () => ({ data: [] }),
+}));
+
+vi.mock("../../components/WidgetConfigDialog", () => ({
+	WidgetConfigDialog: () => <div data-testid="config-dialog-stub" />,
+}));
+
+vi.mock("../../components/WidgetInstance", () => ({
+	WidgetInstanceCard: () => <div data-testid="widget-stub" />,
+}));
+
 import { useDashboardBySlug } from "../../hooks/useDashboards";
 
 function renderPage(slug: string) {
+	const queryClient = new QueryClient({
+		defaultOptions: { queries: { retry: false } },
+	});
 	return render(
-		<MemoryRouter initialEntries={[`/d/${slug}`]}>
-			<Routes>
-				<Route path="/d/:slug" element={<NamedDashboardPage />} />
-			</Routes>
-		</MemoryRouter>,
+		<QueryClientProvider client={queryClient}>
+			<MemoryRouter initialEntries={[`/d/${slug}`]}>
+				<Routes>
+					<Route path="/d/:slug" element={<NamedDashboardPage />} />
+				</Routes>
+			</MemoryRouter>
+		</QueryClientProvider>,
 	);
 }
 
@@ -88,6 +106,26 @@ describe("NamedDashboardPage", () => {
 		} as never);
 		renderPage("empty");
 		expect(screen.getByText("Empty")).toBeInTheDocument();
-		expect(screen.getByText(/no shortcuts yet/i)).toBeInTheDocument();
+		expect(screen.getByText(/This dashboard is empty/i)).toBeInTheDocument();
+	});
+
+	it("renders an edit-widgets button", () => {
+		vi.mocked(useDashboardBySlug).mockReturnValue({
+			data: {
+				id: "d1",
+				label: "Storage",
+				slug: "storage",
+				sort_order: 0,
+				payload: { items: [] },
+				created_at: 1,
+				updated_at: 1,
+			},
+			isLoading: false,
+			isError: false,
+		} as never);
+		renderPage("storage");
+		expect(
+			screen.getByRole("button", { name: /Edit widgets/i }),
+		).toBeInTheDocument();
 	});
 });