Fix notifications

Summary by CodeRabbit

• Refactor

  • Improved notification digest handling to respect frequency settings (immediate, daily, weekly, never).
  • Enhanced logging for better traceability and error reporting.
  • Improved transactional safety during notification processing.

• Bug Fixes

  • Fixed issue where all unsent notifications were previously marked as sent, regardless of their frequency.

• Documentation

  • Added detailed docstrings describing script usage and behavior.