chore(ponytail-mcp): mark private, drop dead bin (#176)

ponytail-mcp reuses the repo's hooks/ via createRequire("../hooks/..."), which
reaches outside the package dir, so it can only run from a checkout (as its
README says), never as a published npm package — a publish tarball wouldn't
include ../hooks/ and would crash. The `bin` field and missing `private` made
it look publishable. Mark it private so an accidental `npm publish` can't ship
a broken package, and drop the dead bin (you point the host at ponytail-mcp/index.js).

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>