Remove self-update, rollback, install, migrate-worktrees, tick, spawn,
register, setup, and repos. These are replaced by Homebrew distribution
(brew upgrade), the agent command, and per-repo .modastack/ config.

Bump to v0.5.0 for the new release.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>