Adds the v0.6.2 Windows installer link pointing to the expected
filename `itsgoin-0.6.2-windows-x64-setup.exe`. Link is live before
the artifact lands so the Windows build pipeline (separate host) has
a stable path to upload to — same pattern we use to coordinate the
Linux / Android builds with the website copy.
Adds `.btn-windows { background: #0078d4 }` to style.css for the
standard four-button download row: Android, Linux AppImage, Linux
CLI, Windows Installer.
738c902287
