PERF.59 Apps: no service worker until someone clicks "Save for offline"; every repeat visit is a cold start minus the 7-day HTTP cache

app-offline.js:160 registers /sw.js only on the click, and sw.js:46 installs nothing on its own; the PWA manifest promises more than the page delivers. Every visit refetches the 830 to 940 KB app page (PERF.2, PERF.3) and relies on the HTTP cache for the 300 to 500 module files (which Vary: Referer defeats, see the server rows). Change: register /sw.js on every /use page; cache-first for immutable URLs (?v= and pinned vendor/app folders: the worker already knows the rule, sw.js:33-40), stale-while-revalidate for the page; "Save for offline" stays the explicit full copy. Pairs with the shared-URL row (a shared lib URL is cached once for all apps) and the installed-package row.