- Add create_setup_token() for PayPal Vault setup token generation
- Add create_payment_token() to exchange setup token for permanent payment token
- Add charge_payment_token() for off-session merchant-initiated transactions
- Update payment_methods table schema with gateway, last4, brand, paypal_email columns
- Update dashboard routes to use new vault flow instead of billing agreements
- No longer requires Reference Transactions to be enabled on PayPal account
- Supports merchant-initiated billing for auto top-ups without user presence