- Created admin_payment_settings.html template with system status dashboard
- Added route /dashboard/admin/payment-settings in main.py
- Implemented GET /api/admin/payment-system/status endpoint (master keys, balances, pending/failed payments)
- Implemented GET /api/admin/payment-system/config endpoint (all payment config)
- Implemented PUT /api/admin/payment-system/config/* endpoints:
  - /price-sources - Configure crypto price sources
  - /blockchain - Configure blockchain monitoring
  - /email - Configure email notifications
  - /consolidation - Configure wallet consolidation
- Added Payment Settings link to admin navigation menu in base.html
- Maintained backward compatibility with legacy POST endpoints