Move cleanup, compact, and reset commands under `bd admin` namespace. Creates hidden aliases for backwards compatibility that show deprecation notice when used. - Create cmd/bd/admin.go with parent command - Create cmd/bd/admin_aliases.go for hidden backwards-compat aliases - Update cleanup.go, compact.go, reset.go to remove rootCmd.AddCommand - Update all documentation to use `bd admin <cmd>` syntax 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>