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/desktop/electron-builder.yml

@@ -49,13 +49,20 @@ linux:
     - rpm
     - tar.gz
 win:
+  artifactName: "Paseo-Setup-${version}-${arch}.${ext}"
   icon: assets/icon.ico
   extraResources:
     - from: bin/paseo.cmd
       to: bin/paseo.cmd
   target:
-    - nsis
-    - zip
+    - target: nsis
+      arch:
+        - x64
+        - arm64
+    - target: zip
+      arch:
+        - x64
+        - arm64
 nsis:
   oneClick: false
   perMachine: false