refactor(payment): code standards fixes and regression repairs

Backend:
- Split payment_order.go (546→314 lines) into payment_order_lifecycle.go
- Replace magic strings with constants in factory, easypay, webhook handler
- Add rate limit/validity unit constants in payment_order_lifecycle, payment_service
- Fix critical regression: add PaymentEnabled to GetPublicSettings response
- Add missing migration 099_fix_migrated_purchase_menu_label_icon.sql

Frontend:
- Fix StripePopupView.vue: replace `as any` with typed interface, use extractApiErrorMessage
- Fix AdminOrderTable.vue: replace hardcoded column labels with i18n t() calls
- Fix SubscriptionsView.vue: replace hardcoded Today/Tomorrow with i18n
- Extract duplicate statusBadgeClass/canRefund/formatOrderDateTime to orderUtils.ts
- Add missing i18n keys: common.today, common.tomorrow, payment.orders.orderType/actions
- Remove dead PurchaseSubscriptionView.vue (replaced by PaymentView)

frontend/src/i18n/locales/en.ts

@@ -308,6 +308,8 @@ export default {
     chooseFile: 'Choose File',
     notAvailable: 'N/A',
     now: 'Now',
+    today: 'Today',
+    tomorrow: 'Tomorrow',
     unknown: 'Unknown',
     minutes: 'min',
     time: {
@@ -5237,6 +5239,8 @@ export default {
       createdAt: 'Created',
       cancel: 'Cancel Order',
       userId: 'User ID',
+      orderType: 'Order Type',
+      actions: 'Actions',
       requestRefund: 'Request Refund',
     },
     result: {