fix: ship prebuilt lib and drop prepare for one-click git install

Avoids pnpm allowBuilds block on dsh plugin add; README install steps expanded for first-time users.

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/auth.js

@@ -0,0 +1,7 @@
+export function isAuthorized(opts) {
+    if (opts.allowAllUsers)
+        return true;
+    if (opts.userId === undefined)
+        return false;
+    return opts.allowedUserIds.includes(opts.userId);
+}