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>

.githooks/pre-commit

@@ -27,7 +27,7 @@ fi
 echo "Running tests..."
 if output=$(./test.sh 2>&1); then
     echo "$output"
-    count=$(sed -n 's/.*\([0-9]\+\) tests: \([0-9]\+\) passed.*/\2 passed/p' <<< "$output")
+    count=$(grep -oP '\d+ passed' <<< "$output" | tail -1)
     write_badge "${count:-passing}" "brightgreen"
 else
     echo "$output"