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>

vite.config.ts

@@ -1,10 +1,20 @@
 import { defineConfig } from "vite";
 import react from "@vitejs/plugin-react";
+import { readFileSync } from "node:fs";
+
+// Bake the package.json version into the bundle so the running SPA can compare
+// it to the server's X-App-Version header and detect a new deploy.
+const appVersion = (
+  JSON.parse(readFileSync("./package.json", "utf8")) as { version: string }
+).version;
 
 export default defineConfig({
   plugins: [react()],
   root: ".",
   publicDir: "public",
+  define: {
+    __APP_VERSION__: JSON.stringify(appVersion),
+  },
   server: {
     port: 3000,
   },