fix: Use PowerShell Expand-Archive for zip extraction on Windows (#190)

The npm postinstall script used `unzip` to extract .zip archives, but
`unzip` is not available by default on Windows, causing installation to
fail with a `spawn UNKNOWN` error. Use PowerShell's `Expand-Archive`
on Windows instead, which is available since PowerShell 5.0 (Windows 10+).

Fixes #187

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

publish/npm/install.js

@@ -109,7 +109,16 @@ function extractArchive(archivePath, extractDir) {
   const isZip = archivePath.endsWith(".zip");
 
   if (isZip) {
-    execSync(`unzip -o "${archivePath}" -d "${extractDir}"`, { stdio: "pipe" });
+    if (process.platform === "win32") {
+      execSync(
+        `powershell -NoProfile -Command "Expand-Archive -Force -Path '${archivePath}' -DestinationPath '${extractDir}'"`,
+        { stdio: "pipe" },
+      );
+    } else {
+      execSync(`unzip -o "${archivePath}" -d "${extractDir}"`, {
+        stdio: "pipe",
+      });
+    }
   } else {
     execSync(`tar -xzf "${archivePath}" -C "${extractDir}"`, { stdio: "pipe" });
   }