chore(changelog): add entry for fee rate update 2026-05 through 2026-08

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+## 2026-05-24 21:58 CEST — feat(fees): update adult monthly rates for 2026-05 through 2026-08
+
+- 2026-05: 700 → 450 CZK; 2026-06/07/08: 600 CZK (new months added).
+- Mirrored in both `scripts/attendance.py` and `go/internal/domain/fees/fees.go`.
+
 ## 2026-05-24 21:42 CEST — feat: multi-account Fio sync + switch QR default to 2502035405/2010
 
 - Added second bank account `2502035405/2010` (IBAN `CZ0820100000002502035405`) to sync.