feat(MemberOrder, MemberOrderHistory, MemberOrderService, OrdersPanel): add paidConfirmed field and update related logic

- Introduced a new boolean field `paidConfirmed` in MemberOrder and MemberOrderHistory models to track payment confirmation status.
- Updated serialization functions in MemberOrderService to include `paidConfirmed` in order and history entries.
- Enhanced OrdersPanel component to allow users to set and display the `paidConfirmed` status for orders.
- Added localization support for the new `paidConfirmed` label in German.
- Adjusted related logic to ensure proper handling of the `paidConfirmed` state throughout the application.

backend/migrations/20260506_add_paid_confirmed_to_member_orders.sql

@@ -0,0 +1,5 @@
+ALTER TABLE `member_orders`
+  ADD COLUMN `paid_confirmed` TINYINT(1) NOT NULL DEFAULT 0 AFTER `budget`;
+
+ALTER TABLE `member_order_history`
+  ADD COLUMN `paid_confirmed` TINYINT(1) NOT NULL DEFAULT 0 AFTER `budget`;