Update "alpha" section to "beta" in website, mention CachyOS in website and page

[Kadynz]

Found two inconsistencies worth fixing:

1. Release stage disagrees: the website warning says the software is in alpha, while the README says beta.
2. CachyOS missing from supported list: it shows up in Releases but isn't in the "Important Notes" section of either the website or the README, which currently lists only Linux Mint 22.3 Cinnamon, Ubuntu 24.04.4 LTS, Kubuntu 24.04.4 LTS, Debian Live 13.3.0 KDE, and Fedora 43 KDE.

Suggestion: align the warning text across website and repo, and add CachyOS to the supported distros list in both.