chore(deps): migrate to react-router 8 and refresh frontend dependencies

react-router-dom 7 is superseded by react-router 8, which folds the DOM
bindings back into the core package. RouterProvider now comes from
`react-router/dom`, while the hooks and `createBrowserRouter` move to
`react-router`. Updates the nine importing modules and the router line in
docs/architecture.md to match.

Also refreshes antd, react-i18next, storybook, eslint, lint-staged and
playwright to current patch/minor releases, and restores alphabetical order
in devDependencies for the @vitest/browser-playwright and playwright entries.

Bumps brace-expansion to 5.0.8, the only release outside the affected range
of GHSA-mh99-v99m-4gvg (unbounded expansion length causing an OOM crash).
`npm audit fix` could not apply this on its own: the lockfile pinned 5.0.7
and npm will not re-resolve a transitive-only dependency in place, so the
entry was updated directly and reinstalled.

docs/architecture.md

@@ -63,7 +63,7 @@ Two key ideas that explain most of the complexity:
 **Frontend (`frontend/`):**
 - **React 19** + **Ant Design 6** + **Vite 8** + **TypeScript**.
 - Data layer: **TanStack Query** (`@tanstack/react-query`) over the native **Fetch API**; **Zod 4** schemas.
-- Router: **react-router-dom 7**. Charts: **uPlot** (`frontend/src/components/viz/Sparkline.tsx`). Editor: **CodeMirror 6**.
+- Router: **react-router 8**. Charts: **uPlot** (`frontend/src/components/viz/Sparkline.tsx`). Editor: **CodeMirror 6**.
 - **Build output goes to `internal/web/dist/`** (see `vite.config.js` → `outDir`) and is
   embedded into the Go binary with `go:embed`. Three HTML entries: `index.html` (panel SPA),
   `login.html`, `subpage.html`. The Go server serves the SPA; there is no separate frontend