Is your feature request related to a problem? Please describe.
Monica currently supports recurring reminders and important dates for fixed intervals (daily, monthly, yearly, etc.), but it does not support more flexible or relative patterns, such as "the 3rd Monday of September" or "last Friday of every month." This limits the ability to set reminders for many real-world scenarios, such as certain holidays, recurring meetings, or events that follow such patterns.

Describe the solution you'd like
It would be extremely helpful if Monica allowed users to create reminders and important dates based on relative date rules. For example:

• 3rd Monday of September
• Last Friday of every month
• 1st Tuesday after the 15th

This could involve adding new fields to the reminder and important date models, updating the UI to support selection of these patterns, and implementing date calculation logic to determine the next occurrence of such dates.

Describe alternatives you've considered (optional)

• Manually updating reminders each year or month (not practical for many users)
• Using external calendar integrations, but those do not sync with Monica's core reminders/tasks

Additional context

• This feature is common in many calendar and reminder systems (e.g., Google Calendar, Outlook)
• Would enable tracking of more complex real-world recurring events
• Useful for holidays, payroll dates, monthly meetings, and more

Thank you for considering this feature!