fix(cli): remove global install postinstall

[shuv1337]

Summary

• replace the generated umbrella package postinstall with a runtime launcher
• preserve platform, architecture, musl, baseline, and AVX2 package selection
• forward CLI arguments and native exit status without lifecycle scripts
• clean stale generated wrapper contents before packing

Verification

• CLI typecheck passed
• launcher and publish-planning tests: 8 passed
• full pre-push typecheck: 32 tasks passed
• isolated packed-tarball bun add --global smoke test reported zero untrusted scripts and executed the real platform binary

Fixes the Blocked 1 postinstall failure from bun i -g shuvcode.