Implement USSD Enhancement with Multi-Level Menus

[llinsss]

Problem

Current USSD implementation is basic. Need advanced multi-level menus, session management, and more features for feature phone users.

Proposed Solution

Build comprehensive USSD system with multi-level menus, balance checks, transaction history, and airtime purchase.

Technical Implementation

New Files:

• backend/services/ussd/MenuBuilder.js - Dynamic menu builder
• backend/services/ussd/SessionManager.js - Session state management
• backend/services/ussd/AirtimeService.js - Airtime purchase
• backend/services/ussd/BillPaymentService.js - Bill payment via USSD
• backend/models/UssdSession.js - Session model
• backend/migrations/20260327000013_create_ussd_sessions.js - Migration
• backend/tests/ussd.enhanced.test.js - Enhanced tests

Modify:

• backend/services/UssdService.js - Add advanced features
• backend/controllers/ussdController.js - Add new menu handlers
• backend/routes/ussd.js - Add new endpoints

USSD Menu Structure

*123# - Main Menu
├── 1. Check Balance
│   ├── 1. Base Chain
│   ├── 2. Starknet
│   ├── 3. Flow
│   ├── 4. Lisk
│   └── 5. U2U
├── 2. Send Money
│   ├── Enter recipient tag
│   ├── Enter amount
│   └── Confirm
├── 3. Transaction History
│   ├── Last 5 transactions
│   └── More...
├── 4. Buy Airtime
│   ├── Enter phone number
│   ├── Enter amount
│   └── Confirm
├── 5. Pay Bills
│   ├── Electricity
│   ├── Water
│   └── Internet
├── 6. My Account
│   ├── My Tag
│   ├── QR Code Link
│   └── Settings
└── 7. Help & Support

Acceptance Criteria

• Multi-level menu navigation
• Session state persistence
• Balance checking for all chains
• Send money via USSD
• Transaction history display
• Airtime purchase integration
• Bill payment integration
• Timeout handling (30 seconds)
• Test coverage > 85%

Priority

High - Critical for feature phone users in Africa