Add AdminTransaction Mongoose model

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/models/AdminTransaction.js

+"use strict";
+var mongoose = require("mongoose");
+var Schema = mongoose.Schema;
+
+var AdminTransactionSchema = new Schema(
+  {
+    merTrxId: { type: String, required: true, unique: true, index: true },
+    transCode: { type: String, required: true },
+    customerName: { type: String, required: true },
+    customerPhone: { type: String, required: true },
+    customerAddress: { type: String, required: true },
+    amount: { type: Number, required: true },
+    payType: { type: String, default: "DC" },
+    status: {
+      type: String,
+      enum: ["pending", "success", "failed"],
+      default: "pending",
+    },
+    merchantToken: { type: String, required: true },
+    timeStamp: { type: String, required: true },
+    resultMsg: { type: String, default: "" },
+    paidAt: { type: Date, default: null },
+  },
+  { timestamps: true }
+);
+
+module.exports = mongoose.model("AdminTransaction", AdminTransactionSchema);