Add service worker implementation and tests for PWA caching strategy

- Implemented a service worker (sw.js) that handles installation, activation, and fetch events.
- Added caching logic for public assets and a fallback for offline navigation.
- Created unit tests (sw.test.ts) to validate service worker behavior, including asset caching, navigation handling, and activation logic.
- Ensured that private API routes and third-party requests are excluded from caching.

src/pwa/manifest.ts

@@ -0,0 +1,9 @@
+import source from "./manifest.webmanifest" with { type: "text" };
+
+export const manifest = JSON.parse(source) as {
+  id: string; name: string; short_name: string; description: string;
+  lang: string; dir: string; start_url: string; scope: string; display: string;
+  background_color: string; theme_color: string; categories: string[];
+  prefer_related_applications: boolean;
+  icons: { src: string; sizes: string; type: string; purpose: string }[];
+};