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.d.ts

@@ -0,0 +1,5 @@
+export declare function isAuthorized(opts: {
+    allowAllUsers: boolean;
+    allowedUserIds: number[];
+    userId?: number;
+}): boolean;