Code changes:
- Show "ℹ️ Nothing to sync" when no notes need syncing (banner instead of toast)
- Add i18n strings for EN/DE
Documentation:
- Improve auto-sync description: mention WiFi reconnect + multi-device sync
- Add 2 new screenshots: server settings & sync status banner
Assets:
- Add screenshots 5 & 6 (server settings & sync banner showcase)