Implement dedup key-based cron tracking to make scheduled jobs resilient to queue
delays. Even if a job is delayed by minutes, it will catch the missed cron window
by tracking previousRunDate in cache instead of relying on isDue() alone.
- Add dedupKey parameter to shouldRunNow() in ScheduledJobManager
- When provided, uses getPreviousRunDate() + cache tracking for resilience
- Falls back to isDue() for docker cleanups without dedup key
- Prevents double-dispatch within same cron window
- Optimize ServerConnectionCheckJob dispatch
- Skip SSH checks if Sentinel is healthy (enabled and live)
- Reduces redundant checks when Sentinel heartbeat proves connectivity
- Remove hourly Sentinel update checks
- Consolidate to daily CheckAndStartSentinelJob dispatch
- Crash recovery handled by sentinelOutOfSync → ServerCheckJob flow
- Add logging for skipped database backups with context (backup_id, database_id, status)
- Refactor skip reason methods to accept server parameter, avoiding redundant queries
- Add comprehensive test suite for scheduling with various delay scenarios and timezones
