feat: ChargeDiscountWallet - callback endpoint, gRPC RPC & service implementation

- Add /api/wallet/verify-discount-charge callback endpoint in PaymentCallbackController
- Add InitiateDiscountCharge RPC + request/response messages in userwallet.proto
- Add InitiateDiscountCharge gRPC service override in UserWalletService
- Add ChargeDiscountWallet using import for handler resolution

src/CMSMicroservice.WebApi/Services/UserWalletService.cs

@@ -4,6 +4,7 @@ using CMSMicroservice.Application.UserWalletCQ.Commands.CreateNewUserWallet;
 using CMSMicroservice.Application.UserWalletCQ.Commands.UpdateUserWallet;
 using CMSMicroservice.Application.UserWalletCQ.Commands.DeleteUserWallet;
 using CMSMicroservice.Application.WalletCQ.Commands.ChargeMagicWallet;
+using CMSMicroservice.Application.WalletCQ.Commands.ChargeDiscountWallet;
 using CMSMicroservice.Application.UserWalletCQ.Queries.GetUserWallet;
 using CMSMicroservice.Application.UserWalletCQ.Queries.GetAllUserWalletByFilter;
 using CMSMicroservice.Application.UserWalletCQ.Queries.GetCustomerWalletChangeLog;
@@ -170,6 +171,27 @@ public class UserWalletService : UserWalletContract.UserWalletContractBase
         };
     }
 
+    // ============= Discount Wallet Methods =============
+
+    public override async Task<InitiateDiscountChargeResponse> InitiateDiscountCharge(
+        InitiateDiscountChargeRequest request, ServerCallContext context)
+    {
+        var userId = GetCurrentUserId();
+
+        var result = await _sender.Send(new ChargeDiscountWalletCommand
+        {
+            UserId = userId,
+            Amount = request.Amount
+        }, context.CancellationToken);
+
+        return new InitiateDiscountChargeResponse
+        {
+            IsSuccess = result.IsSuccess,
+            GatewayUrl = result.GatewayUrl ?? "",
+            ErrorMessage = result.ErrorMessage ?? ""
+        };
+    }
+
     public override async Task<GetMagicWalletStatusResponse> GetMagicWalletStatus(
         Google.Protobuf.WellKnownTypes.Empty request, ServerCallContext context)
     {