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/views/admin/orders/AdminOrdersView.vue

@@ -117,6 +117,7 @@ import { useI18n } from 'vue-i18n'
 import { useAppStore } from '@/stores/app'
 import { adminPaymentAPI } from '@/api/admin/payment'
 import { extractApiErrorMessage } from '@/utils/apiError'
+import { formatOrderDateTime } from '@/components/payment/orderUtils'
 import type { PaymentOrder } from '@/types/payment'
 import AppLayout from '@/components/layout/AppLayout.vue'
 import Pagination from '@/components/common/Pagination.vue'
@@ -233,7 +234,7 @@ async function handleRefund(data: { amount: number; reason: string; deduct_balan
   finally { refundSubmitting.value = false }
 }
 
-function formatDateTime(dateStr: string): string { if (!dateStr) return '-'; return new Date(dateStr).toLocaleString() }
+function formatDateTime(dateStr: string): string { return formatOrderDateTime(dateStr) }
 
 onMounted(() => loadOrders())
 </script>