- bankSyncService: removed local syncDaysBack() reading env directly;
sinceEpoch() now calls getBankSyncConfig().sync_days
- bankSyncConfigService: added setSyncDays() with 1-730 day validation
- routes/admin: PUT accepts sync_days alongside enabled/sync_interval_hours
- BankSyncAdminCard: Transaction history days input, loaded from config,
defaults 90, dirty-checked on save