refactor(web): migrate to data router (createBrowserRouter) to enable useBlocker (#46)

Convert app.tsx route tree verbatim to a module-level data router via
createRoutesFromElements + RouterProvider, and the test harness to
createMemoryRouter + RouterProvider. The search NavLink-click test now mounts
its routes as real data-router routes so RouterProvider intercepts the link
(descendant <Routes> under a catch-all let it fall through to a jsdom navigation).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/test/render.tsx

@@ -1,16 +1,17 @@
 import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
 import { render } from "@testing-library/react";
 import type { ReactElement } from "react";
-import { MemoryRouter } from "react-router-dom";
+import { createMemoryRouter, RouterProvider } from "react-router-dom";
 
 import "../i18n";
 
 export function renderApp(ui: ReactElement, { route = "/" } = {}) {
   const qc = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+  const router = createMemoryRouter([{ path: "*", element: ui }], { initialEntries: [route] });
 
   return render(
     <QueryClientProvider client={qc}>
-      <MemoryRouter initialEntries={[route]}>{ui}</MemoryRouter>
+      <RouterProvider router={router} />
     </QueryClientProvider>,
   );
 }