Fix test cleanup destroying user jobs, consolidate code

- Test cleanup now only removes jobs it created (tracked via
  test_job_ids array) instead of nuking all systab_* units.
  Fixes bug where running tests would delete real user jobs.
- Fix extract_id subshell issue: array appends in $() don't
  propagate to parent, so use _extracted_id variable instead.
- Merge disable_job_by_id/enable_job_by_id into toggle_job_by_id.
- Update usage text: -D/-E/-L/-S now show <id|name> consistently.
- Fix pre-commit hook sed regex that only captured last digit of
  multi-digit numbers; replaced with grep -oP.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

README.md

@@ -167,12 +167,12 @@ Job Creation:
   -m <email>        Send email notification to address (via sendmail)
   -o [lines]        Include job output in notifications (default: 10 lines)
 
-Management:
-  -D <id>           Disable a job
-  -E <id>           Enable a disabled job
+Management (accept hex ID or name):
+  -D <id|name>      Disable a job
+  -E <id|name>      Enable a disabled job
   -e                Edit jobs in crontab-like format
-  -L [id] [filter]  List job logs (optionally for a specific job and/or filtered)
-  -S [id]           Show status of all managed jobs (or a specific job)
+  -L [id|name] [filter]  List job logs (optionally for a specific job and/or filtered)
+  -S [id|name]      Show status of all managed jobs (or a specific job)
   -C                Clean up completed one-time jobs
   -h                Show help
 ```