feat: Refactor SSE implementation and enhance library event handling

Commit notes

This commit updates the Server-Sent Events (SSE) integration in the backend to utilize Elysia's built-in sse() helper for proper event formatting. It improves the event handling in the eventsRoutes, ensuring better error reporting and connection management. Additionally, the sample pack routes are enhanced to publish SSE events upon creation, update, and deletion of sample packs. The frontend is updated to include a new ensureValidToken function for managing access tokens during SSE connections, improving the reliability of real-time updates in the library component.