Adds minimal service worker for PWA installability. On Android Chrome,
the smart banner and install page now trigger the native install dialog
directly instead of showing manual instructions. iOS still shows
step-by-step guide (Apple provides no install API).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Mobile-only install instructions at /zainstaluj-aplikacje with
auto-detected iPhone/Android tabs, CSS UI mockups, and step-by-step
guide. Smart banner appears after 3s on mobile (dismissible via
localStorage), hidden in standalone mode. Footer link and login
page hint also mobile-only.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
