feat: Complete admin panel implementation

- Add user management system with all CRUD operations
- Add promotion statistics dashboard with export
- Simplify Trading & Market settings UI
- Fix promotion schema (dates now optional)
- Add missing API endpoints and PATCH support
- Add comprehensive documentation
- Fix critical bugs (deletePromotion, duplicate endpoints)

All features tested and production-ready.

models/PromoUsage.js

@@ -0,0 +1,112 @@
+import mongoose from "mongoose";
+
+const PromoUsageSchema = new mongoose.Schema(
+  {
+    userId: {
+      type: mongoose.Schema.Types.ObjectId,
+      ref: "User",
+      required: true,
+    },
+    promoId: {
+      type: String,
+      required: true,
+    },
+    promoCode: {
+      type: String,
+      default: null,
+    },
+    promoName: {
+      type: String,
+      required: true,
+    },
+    promoType: {
+      type: String,
+      enum: ["deposit_bonus", "discount", "free_item", "custom"],
+      required: true,
+    },
+    // Bonus received
+    bonusAmount: {
+      type: Number,
+      default: 0,
+    },
+    discountAmount: {
+      type: Number,
+      default: 0,
+    },
+    // Context of usage
+    transactionId: {
+      type: mongoose.Schema.Types.ObjectId,
+      ref: "Transaction",
+      default: null,
+    },
+    depositAmount: {
+      type: Number,
+      default: 0,
+    },
+    // Metadata
+    usedAt: {
+      type: Date,
+      default: Date.now,
+    },
+    ipAddress: {
+      type: String,
+      default: null,
+    },
+  },
+  { timestamps: true }
+);
+
+// Index for quick lookups
+PromoUsageSchema.index({ userId: 1, promoId: 1 });
+PromoUsageSchema.index({ promoId: 1 });
+PromoUsageSchema.index({ userId: 1 });
+
+// Static method to check if user has used a promo
+PromoUsageSchema.statics.hasUserUsedPromo = async function (userId, promoId) {
+  const usage = await this.findOne({ userId, promoId });
+  return !!usage;
+};
+
+// Static method to get user's promo usage count
+PromoUsageSchema.statics.getUserPromoCount = async function (userId, promoId) {
+  return await this.countDocuments({ userId, promoId });
+};
+
+// Static method to get total promo usage count
+PromoUsageSchema.statics.getPromoTotalUses = async function (promoId) {
+  return await this.countDocuments({ promoId });
+};
+
+// Static method to get promo usage stats
+PromoUsageSchema.statics.getPromoStats = async function (promoId) {
+  const stats = await this.aggregate([
+    { $match: { promoId } },
+    {
+      $group: {
+        _id: "$promoId",
+        totalUses: { $sum: 1 },
+        totalBonusGiven: { $sum: "$bonusAmount" },
+        totalDiscountGiven: { $sum: "$discountAmount" },
+        uniqueUsers: { $addToSet: "$userId" },
+        averageBonusPerUse: { $avg: "$bonusAmount" },
+      },
+    },
+  ]);
+
+  if (stats.length === 0) {
+    return {
+      totalUses: 0,
+      totalBonusGiven: 0,
+      totalDiscountGiven: 0,
+      uniqueUsers: 0,
+      averageBonusPerUse: 0,
+    };
+  }
+
+  return {
+    ...stats[0],
+    uniqueUsers: stats[0].uniqueUsers.length,
+  };
+};
+
+export default mongoose.model("PromoUsage", PromoUsageSchema);