chore(test): Playwright für PWA-E2E-Tests aufgesetzt

@playwright/test + chromium als devDep. playwright.config.ts
startet npm run preview (production build nötig für SW), baseURL
localhost:4173, fullyParallel off (SW-Installations-Timing). Ein
Smoke-Test smoke.spec.ts öffnet / und prüft den Titel. test-results/
und playwright-report/ in .gitignore ergänzt.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -12,9 +12,12 @@
     "test:watch": "vitest",
     "lint": "eslint .",
     "format": "prettier --write .",
-    "render:icons": "node scripts/render-icons.mjs"
+    "render:icons": "node scripts/render-icons.mjs",
+    "test:e2e": "playwright test",
+    "test:e2e:ui": "playwright test --ui"
   },
   "devDependencies": {
+    "@playwright/test": "^1.59.1",
     "@sveltejs/adapter-node": "^5.2.0",
     "@sveltejs/kit": "^2.8.0",
     "@sveltejs/vite-plugin-svelte": "^4.0.0",