quick() and dry_run() previously trusted the stored category from
tracked.json without re-validating at delete time. Stale entries from
before #34840 could carry category="cron-output" for cron control-plane
paths (e.g. cron/jobs.json), causing quick() to delete the live
scheduler registry.
Fix:
- Fix guess_category() to only classify cron/output/** as cron-output
(was classifying ALL cron/* paths, missing the #34840 fix).
- Re-validate cron-output entries via guess_category() at delete time
in quick() and dry_run(); stale entries that are no longer classified
as cron-output are skipped and removed from tracked.json.
- Add _is_protected_cron_path() as a hard defense-in-depth guard that
blocks deletion of cron/cronjobs directories and known control-plane
files (jobs.json, .tick.lock) regardless of stored category.
- Update test_cron_subtree_categorised to match fixed guess_category
(only cron/output/* is cron-output, not all of cron/).
Tests: add 5 regression tests in TestStaleCronEntryMigration.