feat(payments): implement PaymentsModule with payment ledger and webhook support

[lishmanTech]

• Add Payment entity with orderId, userId, amount, currency, status, provider, providerReference, metadata, createdAt
• Create enums for PaymentStatus and PaymentProvider
• Implement DTOs for creating and refunding payments
• Add PaymentsService for initiating payments, listing, fetching by id/order, and refunds
• Implement webhook ingestion endpoint for provider-agnostic events
• Add pagination support for admin payment listing
• Register PaymentsModule with controller and service

closes #643

[vercel]

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