feat(sync): add cloud synchronization for favorites

Add a new sync service and frontend integration to allow syncing
favorites across devices using a token.

- Configure `sync-service` in docker-compose.yml on port 7482
- Add sync token input and manual sync button to SideDrawer
- Implement auto-sync logic to persist favorites to the KV store
- Add logic to merge cloud favorites with local data on initialization

docker-compose.yml

@@ -5,4 +5,12 @@ services:
     build: .
     ports:
       - "7481:3000"
+    restart: unless-stopped
+
+  sync-service:
+    build: ./sync-server
+    ports:
+      - "7482:3001"
+    volumes:
+      - ./data:/app/data
     restart: unless-stopped