feat: explicit PWA update prompt with build stamp

- registerType 'prompt' + skipWaiting/clientsClaim false: new SW waits
  instead of silently hijacking running sessions
- main.ts registers via virtual:pwa-register; onNeedRefresh shows
  dismissible toast (i18n en/ru/cu) with Update button -> updateSW(true)
- No polling — update check only on navigation, zero extra traffic
- Settings About shows __BUILD_DATE__ build stamp for remote debugging

src/core/i18n.ts

@@ -12,6 +12,10 @@ export interface Translations {
   error: string;
   notAvailable: string;
 
+  // App update
+  updateAvailable: string;
+  updateReload: string;
+
   // Navigation
   nav: {
     calendar: string;
@@ -548,6 +552,9 @@ const translations: Record<LanguageCode, Translations> = {
     error: 'Error',
     notAvailable: 'Not available',
 
+    updateAvailable: 'New version available',
+    updateReload: 'Update',
+
     nav: {
       calendar: '📅 Calendar',
       service: '📖 Service',
@@ -1116,6 +1123,9 @@ const translations: Record<LanguageCode, Translations> = {
     error: 'Ошибка',
     notAvailable: 'Недоступно',
 
+    updateAvailable: 'Достꙋ́пна новаѧ вєрсі́ѧ',
+    updateReload: 'Обнови́ти',
+
     nav: {
       calendar: '📅 Календарь',
       service: '📖 Устав',
@@ -1684,6 +1694,9 @@ const translations: Record<LanguageCode, Translations> = {
     error: 'Ошибка',
     notAvailable: 'Недоступно',
 
+    updateAvailable: 'Доступна новая версия',
+    updateReload: 'Обновить',
+
     nav: {
       calendar: '📅 Календарь',
       service: '📖 Уставъ',

src/main.ts

@@ -1,5 +1,32 @@
 import './styles/main.css';
+import { registerSW } from 'virtual:pwa-register';
 import { App } from './ui/app';
+import { getTranslations, type LanguageCode } from './core/i18n';
+import { loadSettings } from './ui/settings-view';
+
+const updateSW = registerSW({
+  immediate: true,
+  onNeedRefresh: () => showUpdateToast(),
+});
+
+function showUpdateToast() {
+  if (document.getElementById('pwa-update-toast')) return;
+  const t = getTranslations(loadSettings().language as LanguageCode);
+  const toast = document.createElement('div');
+  toast.id = 'pwa-update-toast';
+  toast.className = 'fixed bottom-4 left-1/2 -translate-x-1/2 z-[60] bg-surface border border-gold/40 rounded-lg shadow-xl px-4 py-3 flex items-center gap-3 max-w-[calc(100vw-2rem)]';
+  toast.innerHTML = `
+    <span class="text-sm text-navy whitespace-nowrap">${t.updateAvailable}</span>
+    <button id="pwa-update-btn" class="bg-gold text-navy rounded px-3 py-1 text-sm font-bold hover:bg-gold-dark transition-colors whitespace-nowrap">${t.updateReload}</button>
+    <button id="pwa-update-dismiss" class="text-navy-light hover:text-navy text-lg leading-none px-1" aria-label="✕">&times;</button>
+  `;
+  document.body.appendChild(toast);
+  toast.querySelector('#pwa-update-btn')?.addEventListener('click', () => {
+    (toast.querySelector('#pwa-update-btn') as HTMLButtonElement).disabled = true;
+    updateSW(true);
+  });
+  toast.querySelector('#pwa-update-dismiss')?.addEventListener('click', () => toast.remove());
+}
 
 const app = new App(document.getElementById('app')!);
 app.init();

src/ui/settings-view.ts

@@ -319,6 +319,7 @@ export class SettingsView {
               ${t.settings.aboutLicense}
             </a>
           </p>
+          <p class="text-[10px] text-navy-light mt-2 opacity-70">build ${__BUILD_DATE__}</p>
         </div>
       </div>
     `;

src/vite-env.d.ts

@@ -1 +1,4 @@
 /// <reference types="vite/client" />
+/// <reference types="vite-plugin-pwa/client" />
+
+declare const __BUILD_DATE__: string;