feat(desktop): build Windows arm64 alongside x64

Multi-arch Windows build in one electron-builder pass, with the website
self-healing across the rename. Asset names go from
`Paseo-Setup-${version}.exe` to `Paseo-Setup-${version}-{x64,arm64}.exe`.

The website now reads the actual installer filename off the latest
GitHub release, so legacy single-arch releases keep rendering a single
"Download" pill while dual-arch releases promote to "Intel / x64" +
"ARM64" automatically. No homepage code change needed when ARM ships.

packages/website/src/components/landing-page.tsx

@@ -1030,9 +1030,9 @@ function GetStarted() {
 }
 
 function DownloadButton() {
-  const { version } = useRelease();
+  const release = useRelease();
   const detectedPlatform = useDetectedPlatform();
-  const primary = getDownloadOptions(version).find((o) => o.platform === detectedPlatform)!;
+  const primary = getDownloadOptions(release).find((o) => o.platform === detectedPlatform)!;
   const PrimaryIcon = primary.icon;
 
   return (