feat: add PWA offline testing documentation and verification (#36)

- Create comprehensive PWA_TESTING.md guide
- Add automated verify-pwa script
- Document all test categories:
  - PWA manifest & installation
  - Service worker functionality
  - Offline mode
  - Cross-platform testing
  - Performance testing
  - Storage management
- Include platform-specific test cases
- Add troubleshooting section
- Create success criteria checklist
- Verify all PWA components present

Testing script checks:
- All icon assets exist
- Screenshots present
- Nuxt config valid
- Composables available
- Components present
- Offline page exists

All automated checks pass ✅

Closes #36

app/package.json

@@ -8,7 +8,8 @@
     "generate": "nuxt generate",
     "preview": "nuxt preview",
     "postinstall": "nuxt prepare",
-    "generate:icons": "node scripts/generate-icons.js && node scripts/generate-screenshots.js"
+    "generate:icons": "node scripts/generate-icons.js && node scripts/generate-screenshots.js",
+    "verify:pwa": "node scripts/verify-pwa.js"
   },
   "dependencies": {
     "@nuxt/fonts": "^0.13.0",