Mobile-first 320–414px (graceful upscale tới 768/1440px). Bottom tab nav 4 tabs,
touch ≥44×44, PWA manifest + Service Worker, Zalo OA notification card primary push channel.
Theo dossier/08-direction-decisions.md §2 Direction D pivot — KHÔNG native app.
manifest.json · sw.js · 17 màn HTML · iconography: lucide-react conventions inlined SVG.