feat: add CashboxExportScheduler for recurring PDF mailing

- Implement CashboxExportScheduler with @Cron(EVERY_DAY_AT_4AM)
- Query due subscriptions (active=true, nextRunDate <= today)
- For each subscription: fetch team, build PDF, send email, advance nextRunDate
- Support monthly/quarterly/yearly intervals via INTERVAL_MONTHS map
- Add cashbox_export_subscription_run to LOGEVENT type for logging
- All 6 tests passing: empty state, monthly/quarterly/yearly periods, multiple subscriptions

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

myteamwallet_backend/src/database/logging/model/logging-event.type.ts

@@ -30,6 +30,7 @@ export type LOGEVENT =
   | 'recurring_transaction_create'
   | 'recurring_transaction_update'
   | 'recurring_transaction_delete'
-  | 'recurring_transaction_run';
+  | 'recurring_transaction_run'
+  | 'cashbox_export_subscription_run';
 
 export type LOGLEVEL = 'FATAL' | 'ERROR' | 'WARN' | 'INFO' | 'DEBUG' | 'TRACE';