feat(pwa): play offline, with updates offered on the map - #55

Summary

The README and AGENTS say the game "works offline"; now it does, following ARCHITECTURE §11 (updated to match what's built).

• Offline: vite-plugin-pwa generates a Workbox service worker that precaches the whole app on the first visit: page, both JS chunks, CSS, the Latin font subsets, manifest (14 entries, ~860 KB before compression; all v1 level data is bundled, so everything is playable offline). Non-Latin font subsets load on demand instead. clientsClaim makes the first worker control the page immediately; without it, a level opened before any reload failed offline (found in the browser check below).
• Updates never interrupt play: registerType: 'prompt', no skipWaiting. platform/AppUpdate records a waiting version; the map (and only the map) shows "A new version of ML Quest is ready." [Update now], which hands over to the new worker and reloads.
• Registration: platform/ServiceWorker uses workbox-window directly (not the plugin's virtual: module, which dependency-cruiser can't resolve, so no rule had to be loosened), only in production builds, and loaded lazily.
• Web app manifest (name, theme colour, SVG icon) and <meta name="theme-color">; the manifest resolves under /ml-quest/ on Pages.

Dependencies (RULES §10)

• workbox-window 7.4.1 (runtime): registers the worker and handles the update hand-off. 2.2 kB gzip, in a lazy chunk: first load stays 163.8 / 170 kB.
• vite-plugin-pwa 1.3.0 (dev only): generates sw.js and the manifest at build time; supports Vite 8.

Verification

• typecheck, lint, format, 350 tests (AppUpdate: an update waits until asked, then applies with reload; app test: the banner appears on the map but not on a level, and "Update now" applies it), 118 pass-bot runs, levels:validate, build, size: all green.
• Browser check on a production build with the server stopped: the worker installs on the first visit (12 files cached) and controls the page; then, offline, opening Draw the Line from the running page works, and a full fresh load of #/w/2/l/5 renders Tame It completely.
• Update flow in a real browser: served a temporary "v2" build; the open app kept showing v1 (no auto-reload) and the map showed the banner; "Update now" switched to v2 with progress intact. The temporary change was reverted and the test worker and cache removed.

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