Wire `core module install/remove/list/update` commands to the
marketplace.Installer from pkg/marketplace. Follows the exact
pattern established by cmd/plugin/.
- install: clone from Git repo with optional ed25519 verification
- list: table output of installed modules
- update: pull latest + re-verify manifest (supports --all)
- remove: confirmation prompt then cleanup
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
