Implement the core report generation that:
- Loads .streamd.toml configuration
- Calculates expected hours based on periods and day types
- Calculates actual hours following day type rules:
- Sick leave: max(expected, worked)
- Vacation: expected + worked
- Flex day: 0
- Holiday: 0 expected
- Generates warnings for missing days, overlapping timecards,
and work outside configured periods
- Calculates monthly and cumulative balances
- Sorts months in descending order
