Add 6-char hex short IDs (SYSTAB_ID) embedded in unit files for
human-friendly job identification. The -E flag now opens a real
crontab-like editor where jobs can be created, updated, and deleted
by editing tab-separated ID/SCHEDULE/COMMAND lines. Legacy jobs
without IDs get one auto-assigned on first edit.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
