refactor: implement minimal PWA caching strategy

- Cache only essential PWA assets (manifest, icons, core scripts)
- Use Network First for all other requests
- Remove aggressive caching of UI components and styles
- Preserve PWA installation while minimizing cache footprint

index.html

@@ -157,6 +157,7 @@
 <script src="src/scripts/pwa-register.js"></script>
 <script src="./src/pwa/install-prompt.js" type="module"></script>
 <script src="./src/pwa/pwa-manager.js" type="module"></script>
+<script src="./src/scripts/pwa-offline-test.js"></script>
 <link rel="stylesheet" href="./src/styles/pwa.css">
 </body>
 </html>