feat: task 1.7 routing skeleton

TanStack Router file-based routes:
- vite.config.ts: TanStackRouterVite plugin (target: react,
  autoCodeSplitting: true) before the React plugin.
- .gitignore: src/routeTree.gen.ts (auto-generated).
- src/lib/query-client.ts: module-level QueryClient singleton.
- src/routes/__root.tsx: root route, QueryClientProvider, Suspense-
  wrapped router + query devtools (dev-only via import.meta.env.DEV).
- src/routes/login.tsx: public route. validateSearch schema accepts
  optional redirect. LoginRoute wraps <LoginPage> with onAuthenticated
  navigating to redirect ?? '/'.
- src/routes/_authed/route.tsx: pathless protected layout. beforeLoad
  redirects to /login on 'anonymous'; falls through on 'unknown' /
  'authenticating' so hard reload doesn't flash the login page.
- src/routes/_authed/index.tsx: placeholder home with sign-out button.
  Cross-tab logout effect bounces to /login on store transition.
- src/App.tsx: replaced — now creates the router and renders
  <RouterProvider />. The interim status-branching logic from 1.6 is
  gone (the route tree handles it).
- eslint.config.js: override for src/routes/** disabling
  react-refresh/only-export-components — TanStack Router's file-based
  pattern intentionally co-exports Route alongside components.

Code-splitting working: login chunk 37KB, home + auth 17KB, card
primitive 31KB, all loaded lazily; main bundle 353KB.

Deviations:
1. No top-level useRequireAuth hook — per-page useEffect on store
   transitions is just as effective and only used in one place.
2. ESLint override for src/routes/** matches the existing pattern for
   src/ui/primitives/**.
3. Login page's auto-navigate effect from 1.6 is removed — the route
   wrapper owns navigation via onAuthenticated.

eslint.config.js

@@ -29,4 +29,13 @@ export default defineConfig([
       'react-refresh/only-export-components': 'off',
     },
   },
+  {
+    // TanStack Router file-based routes export `Route` (the route definition)
+    // alongside the route's component. That's the canonical pattern; the
+    // fast-refresh rule doesn't apply usefully here.
+    files: ['src/routes/**/*.{ts,tsx}'],
+    rules: {
+      'react-refresh/only-export-components': 'off',
+    },
+  },
 ]);