Phase 1: workflow subcommand group (add/list/show/rm/history/rollback)
Phase 2: thread subcommand group (run/list/show/rm/fork/ps/kill/live/pause/resume)
Phase 3: cas gc + top-level aliases + deprecation warnings for old flat commands
- Follow existing CAS_SUBCOMMAND_TABLE pattern for workflow and thread groups
- Top-level 'run' and 'live' stay as shortcuts (no deprecation)
- Old flat commands print deprecation warning then delegate
- Update usage string to show grouped format
- Update tests to use new grouped syntax