Configured-month cases now read expected values from AdultFeeMonthlyRate /
JuniorFeeMonthlyRate via a mustRate helper that panics if a test month is
removed from the map. Fallback cases use AdultFeeDefault / JuniorFeeDefault.
This way the tests verify dispatch logic (0/1/2+ branching, map vs. fallback)
without breaking when rates are intentionally updated in the map.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Ports calculate_fee and calculate_junior_fee from scripts/attendance.py
into a new go/internal/domain/fees package. Introduces the Expected type
(Value int, Unknown bool) for the junior "?" sentinel, keeping the Go
API strictly typed instead of mirroring Python's str|int return.
All 20 table-driven tests pass with -race; golangci-lint clean.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
