feat: sync crontab on init and clean test artifacts

[avoidwork]

Description

Implement automatic reconciliation of persisted job definitions (memory/schedules/*.json) with the system crontab on every container init. Jobs persist between container updates without duplication or interruption of running crond jobs.

Additionally, cronjob tests now clean the system crontab after each run by calling Cron.uninstall() in the after() hook, ensuring no residual madz-schedules block entries linger.

Type of Change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactor (no functional change)
• Performance improvement
• CI / build / tooling

Testing

Unit tests (tests/unit/cron_sync.test.js — 12 tests):

• Adds a job that exists on disk but not in crontab
• Removes a job that exists in crontab but not on disk
• Updates a job with differing cron expression
• Updates a job with differing command
• Excludes paused jobs from crontab
• Idempotent: produces identical crontab on repeated calls
• Preserves lines outside the madz block
• Handles empty schedules directory
• Handles empty crontab
• Handles jobs with no command field (skips them)
• Handles non-existent schedules directory gracefully
• Syncs multiple jobs correctly

Integration tests (tests/integration/sync_integration.test.js — 4 tests):

• Create a job via cronjob tool, verify job appears in crontab after sync
• Remove a job via cronjob tool, verify job is removed from crontab after sync
• Update a job cron expression via cronjob tool, verify updated cron in crontab after sync
• Disable sync via config, verify no crontab changes on restart

Test hygiene (tests/unit/tools_cron.test.js):

• Import Cron scheduler and call uninstall() in after() hook to strip the entire madz-schedules block from the system crontab after all cronjob tests complete.

All 16 new tests pass. Full test suite passes (100% of existing tests unaffected).

Coverage

• 100% line coverage maintained — pre-commit hook verified

Checklist

• npm run lint passes — oxlint + oxfmt clean
• Tests pass with 100% line coverage — 16 new tests, all pass
• No forbidden patterns used — no console.log in prod (uses console.warn/log with oxlint-disable), no empty catches, no eval
• Conventional Commit style applied

Archive Status

Change sync-crond-on-init has been archived. The new crontab-sync capability spec has been merged into the main specs directory.