BREAKING CHANGE: Payment due dates now follow advance payment schedule:
- Q1 payments: Due December 15 of previous year
- Q2 payments: Due March 15 of same year
- Q3 payments: Due June 15 of same year
- Q4 payments: Due September 15 of same year
Changes:
- Updated create_quarterly_support_payment() to use advance schedule
- Enhanced diagnostic commands to check advance payment dates
- Added fix_advance_payment_dates command for comprehensive fixes
- Updated fix_q4_payment_dates to correct Q4 from 31.12 to 15.09
This aligns with semester-based document submissions while maintaining
the advance payment system where payments are made before each quarter.
Jan Remmer Siebels
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