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/server.ts

@@ -7,6 +7,7 @@ import rateLimit from "@fastify/rate-limit";
 import path from "path";
 import { config } from "./config/env";
 import { securityHeaders } from "./middleware/security";
+import { registerVersionHeader } from "./middleware/version";
 import prisma from "./config/database";
 
 import authRoutes from "./routes/admin/auth";
@@ -100,6 +101,9 @@ async function start() {
   // --- Security headers ---
   app.addHook("onRequest", securityHeaders);
 
+  // --- Version header: lets the SPA detect a new deploy and prompt a refresh ---
+  registerVersionHeader(app);
+
   // --- Global error handler — consistent { success, error } format ---
   app.setErrorHandler(
     (err: Error & { statusCode?: number }, request, reply) => {