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/components/payment/orderUtils.ts

@@ -0,0 +1,34 @@
+/**
+ * Shared utility functions for payment order display.
+ * Used by AdminOrderDetail, AdminOrderTable, AdminRefundDialog, AdminOrdersView, etc.
+ */
+
+const STATUS_BADGE_MAP: Record<string, string> = {
+  PENDING: 'badge-warning',
+  PAID: 'badge-info',
+  RECHARGING: 'badge-info',
+  COMPLETED: 'badge-success',
+  EXPIRED: 'badge-secondary',
+  CANCELLED: 'badge-secondary',
+  FAILED: 'badge-danger',
+  REFUND_REQUESTED: 'badge-warning',
+  REFUNDING: 'badge-warning',
+  PARTIALLY_REFUNDED: 'badge-warning',
+  REFUNDED: 'badge-info',
+  REFUND_FAILED: 'badge-danger',
+}
+
+const REFUNDABLE_STATUSES = ['COMPLETED', 'PARTIALLY_REFUNDED', 'REFUND_REQUESTED', 'REFUND_FAILED']
+
+export function statusBadgeClass(status: string): string {
+  return STATUS_BADGE_MAP[status] || 'badge-secondary'
+}
+
+export function canRefund(status: string): boolean {
+  return REFUNDABLE_STATUSES.includes(status)
+}
+
+export function formatOrderDateTime(dateStr: string): string {
+  if (!dateStr) return '-'
+  return new Date(dateStr).toLocaleString()
+}