V12 - Wallet migration + NayaPay temporary OFF

- One-time migration converts every existing Normal/blank customer to Wallet customer. Existing wallet balances, orders and history are preserved.
- New admin-created customers default to Wallet.
- NayaPay is set to Inactive once during this upgrade; its account/details and verification code are NOT deleted.
- Re-enable NayaPay any time from Admin > Payment Methods by editing NayaPay and setting Status = Active.
- TOPUP payment method list is now dynamic. Disabled methods do not appear and numbering closes automatically.
- PAYMENT command also hides NayaPay while its Payment Methods status is inactive.
