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/lib/dashboard.ts

@@ -14,6 +14,8 @@ export async function habitRequest<T>(
   path: string,
   options?: RequestInit,
 ): Promise<T> {
+  if (typeof navigator !== "undefined" && navigator.onLine === false)
+    throw new Error("You’re offline. Reconnect and try again. Changes have not been saved or queued.");
   const response = await fetch(`/api${path}`, options);
   if (!response.ok) {
     if (response.status === 401)