fix: mark beta-tools as private to skip npm publish

beta-tools is an internal CLI tool and should not be published to npm.
The beta publish workflow was failing with E404 because the
@bitgo-beta/beta-tools package does not exist on the registry and
trusted publishing cannot create new packages.

Ticket: BTC-0

Author: lcovar

modules/beta-tools/package.json

@@ -36,8 +36,6 @@
       "yarn eslint --fix"
     ]
   },
-  "publishConfig": {
-    "access": "public"
-  },
+  "private": true,
   "license": "MIT"
 }