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

playwright.pwa.config.ts

@@ -0,0 +1,29 @@
+/// <reference types="node" />
+
+// TEMPORARY: verification harness for the PWA offline/update behaviour.
+// The spec starts the production `node build/index.js` server itself, because a "deployment"
+// has to restart the process (adapter-node caches build-file stats at startup).
+import { defineConfig } from '@playwright/test';
+import { existsSync } from 'node:fs';
+
+const chromiumExecutable =
+	process.env.PLAYWRIGHT_CHROMIUM_EXECUTABLE_PATH ??
+	(existsSync('/usr/bin/chromium') ? '/usr/bin/chromium' : undefined);
+
+export default defineConfig({
+	testDir: './tests/e2e',
+	testMatch: 'pwa.spec.ts',
+	fullyParallel: false,
+	workers: 1,
+	retries: 0,
+	reporter: 'list',
+	timeout: 420_000,
+	use: {
+		baseURL: 'http://127.0.0.1:4179',
+		trace: 'retain-on-failure',
+		launchOptions: {
+			executablePath: chromiumExecutable,
+			args: ['--no-sandbox']
+		}
+	}
+});