macOS virtual files client article update for release 33.0.0

- Removed obsolete information about the different macOS builds for classic synchronization and file provider extension because we now have only one universal macOS client left.
- Clarified the conflict between the classic folder synchronization integration and file provider extension.
- Clarified the benefits of enabling push notifications on the server side.
- Updated feature list.
- Updated screenshots with a consistent appearance based on macOS 26 Tahoe and demo content.
- Screenshots are now in optimized JPG format instead of PNG. There is no notable quality loss but the image sizes are drastically reduced.

Signed-off-by: Iva Horn <iva.horn@nextcloud.com>

Author: i2h3