The PWA already existed but nothing told a mobile visitor it could be
installed - Chrome own default mini-infobar is easy to miss, and
Safari has no browser-driven prompt at all. New pwaInstall.ts (self-
mounting like toast.ts) captures beforeinstallprompt as early as
possible (a top-level side effect of importing the module from
Shell.ts, live before boot() even starts its async login check, since
that event never replays for a listener that attached too late) and
shows a banner with a real Installer button on Chrome/Edge/Android, or
manual Share-then-home-screen instructions on iOS Safari where no such
event exists at all. Mobile-only, suppressed once already running
standalone, and a close click remembers not to ask again.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
