feat(app): detect new deploy and prompt refresh (+ lazy-chunk recovery)

When a new version is deployed, open tabs no longer silently run stale code
until a manual F5.

- Server stamps every response with X-App-Version (src/middleware/version.ts,
  onSend hook in server.ts).
- Client bakes its build version via Vite define (__APP_VERSION__); apiFetch
  compares the header to it (no polling — piggybacks existing traffic) and
  latches a mismatch in a small store (appVersion.ts).
- UpdateBanner: a persistent bottom Snackbar "Je k dispozici nová verze
  aplikace. — Obnovit" → location.reload(). User-initiated, so an in-progress
  form is never interrupted.
- lazyWithReload: every React.lazy page reloads once if its hashed chunk 404s
  after a deploy (sessionStorage-guarded against loops), fixing the "old chunk
  gone" error screen.

Approach chosen after researching current SPA practice (version header + banner
beats polling / a service worker for a non-PWA admin app).

Tests: +4 (server header, client store latch/notify). Full suite 669 pass,
tsc -b clean, lint 0. Verified live via Playwright (header emitted; banner
appears on a simulated mismatch). Detection applies to deploys from the NEXT
release onward (current clients lack the detection code).

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

src/admin/utils/api.ts

@@ -1,3 +1,5 @@
+import { reportServerVersion } from "./appVersion";
+
 class ApiState {
   showSessionExpiredAlert = false;
   showLogoutAlert = false;
@@ -120,6 +122,8 @@ export const apiFetch = async (
     headers,
     credentials: "include",
   });
+  // Detect a new deploy: compare the server's build version to ours.
+  reportServerVersion(response.headers.get("X-App-Version"));
 
   if (response.status === 401 && state.refreshFn) {
     // If the caller already unmounted (TanStack Query aborted the request),