pwa / offline mode

- @vite-pwa/sveltekit: workbox precache (incl. pdfjs worker), generated manifest, prompt-style updates via PwaUpdatePrompt toast
- prerendered routes for offline navigation, PWA icons, theme-color + apple-touch-icon
- pwa offline/update e2e suite (pnpm test:pwa, playwright.pwa.config.ts)
- datenschutz: offline/install section; prettier cleanup of shadcn components

TODO.md

@@ -0,0 +1,17 @@
+# PWA / Offline-Fähigkeit (plan/pwa-plan.md)
+
+- [x] Add `@vite-pwa/sveltekit` dev dependency (pnpm, plus explicit `vite-plugin-pwa`/`workbox-window` for pnpm strict resolution)
+- [x] Generate PWA icons (192 / 512 / maskable / apple-touch) from `static/favicon.svg`
+- [x] Configure `SvelteKitPWA` in `vite.config.ts` (manifest, workbox glob patterns incl. pdfjs `.mjs` worker, navigateFallback)
+- [x] Enable prerendering so route documents are precached (`src/routes/+layout.ts`)
+- [x] Add PWA client type references (`src/app.d.ts`)
+- [x] Update toast component + `virtual:pwa-info` manifest link in root layout
+- [x] Add `theme-color` meta + apple-touch-icon
+- [x] Production-build verification: SW registers, offline document/tool navigation, offline ZIP + merge chain, update toast (defer + activate) — `pnpm test:pwa`
+- [x] Run `pnpm check` (0 errors), `pnpm build`
+- [x] Update `agents.md`
+- [x] `pnpm lint`: 19 formatting failures fixed via `pnpm format` (shadcn-generated
+      `src/lib/components/ui/` and `src/lib/components/icons/`, plus `AttachmentPreview.svelte`;
+      pure reformatting, no logic changes)
+- [ ] `datenschutz` wording: draft added to section 4 (“Offline-Nutzung als App (Progressive Web
+      App)”) in `src/routes/datenschutz/+page.svelte` — pending user review/approval (D3)