V64 PWA update

Added:
- public/manifest.webmanifest
- public/service-worker.js
- public/offline.html
- public/assets/img/pwa/icon-192.png
- public/assets/img/pwa/icon-512.png
- public/assets/img/pwa/icon-192-maskable.png
- public/assets/img/pwa/icon-512-maskable.png
- PWA meta tags in app/Views/layouts/main.php
- Install app button in hamburger menu: app/Views/components/header.php
- PWA install prompt handler and service worker registration in public/assets/js/app.js
- PWA toast styles in public/assets/css/app.css

Important host note:
PWA installation requires HTTPS on production domains.