v2.0.0

feat: landing page on Netlify and GitHub Release packages for every OS

Static site in site/ with a live demo of the real app UI, OS-aware
download links from the latest release, and a strict CSP. CI now
attaches dmg/exe/msi/deb/rpm/AppImage to v* tag releases.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>