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.

bun-env.d.ts

@@ -9,6 +9,10 @@ declare module "*.svg" {
 }
 
 declare module "*.css" {}
+declare module "*.webmanifest" {
+  const content: string;
+  export default content;
+}
 declare module "*.png" {
   const path: string;
   export default path;