Initial backend code

src/models/Equity.js

@@ -0,0 +1,80 @@
+const mongoose = require('mongoose');
+
+const equitySchema = new mongoose.Schema({
+  title: {
+    type: String,
+    required: true,
+    trim: true
+  },
+  description: {
+    type: String,
+    default: ''
+  },
+  type: {
+    type: String,
+    enum: ['coupon', 'membership', 'discount', 'gift', 'other'],
+    required: true
+  },
+  platform: {
+    type: String,
+    required: true,
+    enum: ['taobao', 'jd', 'pdd', 'meituan', 'eleme', 'douyin', 'kuaishou', 'other']
+  },
+  value: {
+    type: Number,
+    default: 0
+  },
+  unit: {
+    type: String,
+    default: '元'
+  },
+  validStart: {
+    type: Date,
+    required: true
+  },
+  validEnd: {
+    type: Date,
+    required: true
+  },
+  status: {
+    type: String,
+    enum: ['active', 'used', 'expired', 'transferred'],
+    default: 'active'
+  },
+  owner: {
+    type: mongoose.Schema.Types.ObjectId,
+    ref: 'User',
+    required: true
+  },
+  source: {
+    type: String,
+    enum: ['manual', 'import', 'purchase', 'transfer'],
+    default: 'manual'
+  },
+  images: [{
+    type: String
+  }],
+  tags: [{
+    type: String
+  }],
+  isTransferable: {
+    type: Boolean,
+    default: true
+  },
+  transferPrice: {
+    type: Number,
+    default: 0
+  },
+  metadata: {
+    type: mongoose.Schema.Types.Mixed,
+    default: {}
+  }
+}, {
+  timestamps: true
+});
+
+equitySchema.index({ owner: 1, status: 1 });
+equitySchema.index({ platform: 1, type: 1 });
+equitySchema.index({ validEnd: 1 });
+
+module.exports = mongoose.model('Equity', equitySchema);