- Separate fetchedAt (immutable) and scheduledAt (mutable) timestamps
- Add custom JsonDeserializer to ensure fetchedAt is set by constructor
- Add transient fetchTime field for Gson compatibility
- Update TTL enforcer to use fetchedAt for freshness checks
- Increase DEFAULT_TTL_SECONDS to 25 hours for daily notifications
- Update storage to use custom Gson deserializer
- Add debug logging for timestamp validation
- Fix timestamp initialization in NotificationContent constructor
This resolves the TTL_VIOLATION error that was preventing
notifications from being scheduled due to stale timestamp data.