Support Custom Monthly Scan Scheduling

We would like more flexible monthly scan scheduling options. Currently, selecting "monthly" triggers scans every 30 days, which can cause schedule drift and potentially skip a month due to varying month lengths.

We would like the ability to schedule scans based on specific calendar patterns, such as:

• The 1st of the month

• The 2nd Tuesday of each month

• The last Friday of the month
  

This feature would help ensure consistency in scan timing and better alignment with internal reporting and compliance cycles.