Add zooming/scaling settings.

### Issue Details

On what is in 2026 a reasonably sized monitor setup, with the Windows 11 scaling set to the standard 100%, pretty much everything in the AdGuard settings is too small in fullscreen mode.

How it looks like on a circa 2880x2300px setup:

Test environment:
* AdGuard version: 8.0.5436.0
* OS: Windows 11 25H2 Pro for Workstations x64

### Proposed solution

Add settings to enlarge things in the app by 150%/200%/250%.

### Alternative solution

None that I know of.