feat: improve worktree flow, subcommand help, and CLI docs

[EndersonPro]

Summary

• improve create flow with optional pre-sync prompt and correct behavior when user chooses No
• restore and keep package selection in interactive stepper while preserving non-interactive --package/--package-base
• add add-repo service support for post-create repo attachment and root-file copying helpers
• add interactive loading feedback for pubget
• standardize subcommand help behavior (--help/-h) and expand CLI contract coverage
• document recent CLI adjustments clearly in README

Validation

• updated/added unit and integration tests in Go for the new CLI contract and create workflow behavior