Offline PWA: service worker + offline app shell

[rec3141]

Part of #1.

Register a service worker via vite-plugin-pwa (Workbox). Today static/manifest.json exists and is linked in app.html, but no service worker is registered — this is step 0 of the offline PWA.

Scope

• Add vite-plugin-pwa; generate + register the service worker.
• Precache the app shell so the wizard renders offline.
• Precache/runtime-cache the data the wizard needs offline: the MIxS glossary JSON, the lab's picklists, and its projects + sites list.
• Versioning/update strategy so a new deploy refreshes the cache without stranding queued offline data.

Done when

• Loading the wizard route with the network off renders the form fully (shell + glossary + picklists + project/site lists).