Extract CLI operations into a service layer and add non-interactive flags

[c0rychu]

Current Typer commands perform filesystem mutations directly and rely on interactive prompts (typer.confirm). That makes automation/CI awkward and mixes CLI concerns with operational logic. Proposal: introduce a small service layer (e.g., link_project / garbage_collect) that accepts dry-run and force/yes flags; have the CLI delegate to it; add --yes/--force options for non-interactive use; expand tests to cover both prompt and non-prompt paths.