新增农户功能升级：身份证OCR/OSS上传、头像采集、同名村检测、Region热度排序及表单体验优化

- Region 表新增热度列，热门省份优先显示
- 区县下拉按地级市分组、已录区县优先、支持全省搜索
- 组选择内置一组至二十组
- 银行卡号独立行+粗体预览，开户行独立行
- 新增农户类型：农户/个体户/合作社/经营集体/公司
- 身份证正反面支持高拍仪/摄像头OCR与手机扫码上传，附件存本地/OSS
- 新增农户头像采集组件（摄像头/本地上传），预留人脸识别收购扩展
- 同名村弹窗提醒（防选错乡镇）
- 编辑窗体禁止遮罩/Esc误关，整体加宽适配高频操作
- 修复二维码局域网手机无法访问（监听0.0.0.0、局域网IP识别、Vite代理兜底）

backend/AgriculturalPlatform.Api/Models/PurchaseOrder.cs

@@ -0,0 +1,67 @@
+namespace AgriculturalPlatform.Api.Models;
+
+/// <summary>收购单（过磅称重单）</summary>
+public class PurchaseOrder
+{
+    public int Id { get; set; }
+
+    /// <summary>收购单号（如 CG20260812-0001）</summary>
+    public string OrderNo { get; set; } = string.Empty;
+
+    /// <summary>农户</summary>
+    public int FarmerId { get; set; }
+
+    public Farmer? Farmer { get; set; }
+
+    /// <summary>收购品种</summary>
+    public int ProductId { get; set; }
+
+    public Product? Product { get; set; }
+
+    /// <summary>收购方组织（公司/站/个体）</summary>
+    public int PurchaserOrgId { get; set; }
+
+    public Organization? PurchaserOrg { get; set; }
+
+    /// <summary>等级（一等/二等/三等）</summary>
+    public string Grade { get; set; } = string.Empty;
+
+    public string Unit { get; set; } = "公斤";
+
+    /// <summary>单价（元/单位）</summary>
+    public decimal UnitPrice { get; set; }
+
+    /// <summary>毛重（kg）</summary>
+    public decimal GrossWeight { get; set; }
+
+    /// <summary>皮重（kg）</summary>
+    public decimal TareWeight { get; set; }
+
+    /// <summary>净重（kg）= 毛重 - 皮重</summary>
+    public decimal NetWeight { get; set; }
+
+    /// <summary>金额（元）= 净重 × 单价</summary>
+    public decimal Amount { get; set; }
+
+    /// <summary>过磅次数：1=已称毛重，2=已回皮完成</summary>
+    public int WeighCount { get; set; }
+
+    public PurchaseStatus Status { get; set; } = PurchaseStatus.Weighing;
+
+    /// <summary>经办人</summary>
+    public int? OperatorId { get; set; }
+
+    public User? Operator { get; set; }
+
+    /// <summary>第一次过磅时间（进场称毛重）</summary>
+    public DateTime WeighInAt { get; set; } = DateTime.Now;
+
+    /// <summary>回皮时间</summary>
+    public DateTime? WeighOutAt { get; set; }
+
+    public string Notes { get; set; } = string.Empty;
+
+    public DateTime CreatedAt { get; set; } = DateTime.Now;
+
+    public DateTime? UpdatedAt { get; set; }
+}