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/routes/__root.tsx

@@ -6,13 +6,19 @@ import { getStarCount } from "~/stars";
 
 interface ReleaseContext {
   version: string;
+  windowsX64Asset: string | null;
+  windowsArm64Asset: string | null;
 }
 
 interface StarsContext {
   stars: string;
 }
 
-const ReleaseCtx = createContext<ReleaseContext>({ version: "" });
+const ReleaseCtx = createContext<ReleaseContext>({
+  version: "",
+  windowsX64Asset: null,
+  windowsArm64Asset: null,
+});
 const StarsCtx = createContext<StarsContext>({ stars: "" });
 
 const PLAUSIBLE_INIT_SCRIPT = {