* update selfhst icon-URLs to use @master path
Changed all icon URLs in JSON files from 'cdn.jsdelivr.net/gh/selfhst/icons/webp/' to 'cdn.jsdelivr.net/gh/selfhst/icons@master/webp/' for consistency and to ensure the latest icons are referenced.
* added missing icons
Added explicit warnings and user confirmation prompts to install scripts that run external installers from third-party sources. Updated JSON metadata to remove warning notes about external sources, as the scripts now handle user notification and consent directly. This improves transparency and user safety during installation.
