Implement comprehensive topup billing system with user history viewing and admin management capabilities.
## Features Added
### Frontend
- Add topup history modal with paginated billing records
- Display order details: trade number, payment method, amount, money, status, create time
- Implement empty state with proper illustrations
- Add payment method column with localized display (Stripe, Alipay, WeChat)
- Add admin manual completion feature for pending orders
- Add Coins icon for recharge amount display
- Integrate "Bills" button in RechargeCard header
- Optimize code quality by using shared utility functions (isAdmin)
- Extract constants for status and payment method mappings
- Use React.useMemo for performance optimization
### Backend
- Create GET `/api/user/topup/self` endpoint for user topup history with pagination
- Create POST `/api/user/topup/complete` endpoint for admin manual order completion
- Add `payment_method` field to TopUp model for tracking payment types
- Implement `GetUserTopUps` method with proper pagination and ordering
- Implement `ManualCompleteTopUp` with transaction safety and row-level locking
- Add application-level mutex locks to prevent concurrent order processing
- Record payment method in Epay and Stripe payment flows
- Ensure idempotency and data consistency with proper error handling
### Internationalization
- Add i18n keys for Chinese (zh), English (en), and French (fr)
- Support for billing-related UI text and status messages
## Technical Improvements
- Use database transactions with FOR UPDATE row-level locking
- Implement sync.Map-based mutex for order-level concurrency control
- Proper error handling and user-friendly toast notifications
- Follow existing codebase patterns for empty states and modals
- Maintain code quality with extracted render functions and constants
## Files Changed
- Backend: controller/topup.go, controller/topup_stripe.go, model/topup.go, router/api-router.go
- Frontend: web/src/components/topup/modals/TopupHistoryModal.jsx (new), web/src/components/topup/RechargeCard.jsx, web/src/components/topup/index.jsx
- i18n: web/src/i18n/locales/{zh,en,fr}.json
