fix: 修复页面间状态丢失问题并优化选择页面

- 修复选择审批人后再选择抄送人导致状态丢失的问题
- 使用独立的 sessionStorage key (selectedApprovers, selectedCc)
- 组件每次挂载时从 sessionStorage 恢复状态
- 只在提交/保存成功后清除 sessionStorage
- 优化人员选择页面布局和样式
- 更新 CLAUDE.md 文档记录问题和解决方案

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/Model/ApprovalRecord.php

@@ -0,0 +1,63 @@
+<?php
+
+namespace App\Model;
+
+use Illuminate\Database\Eloquent\Model;
+
+class ApprovalRecord extends Model
+{
+    protected $table = 'approval_record';
+
+    protected $fillable = [
+        'order_id',
+        'node_id',
+        'node_type',
+        'approver_id',
+        'action',
+        'comment',
+    ];
+
+    protected $casts = [
+        'created_at' => 'datetime',
+    ];
+
+    /**
+     * 操作类型常量
+     */
+    const ACTION_SUBMIT = 'submit';   // 提交
+    const ACTION_APPROVE = 'approve'; // 通过
+    const ACTION_REJECT = 'reject';   // 拒绝
+    const ACTION_CANCEL = 'cancel';   // 撤销
+
+    /**
+     * 关联审批单
+     */
+    public function order()
+    {
+        return $this->belongsTo(ApprovalOrder::class, 'order_id');
+    }
+
+    /**
+     * 关联审批人
+     */
+    public function approver()
+    {
+        return $this->belongsTo(User::class, 'approver_id');
+    }
+
+    /**
+     * 判断是否是批准操作
+     */
+    public function isApproved(): bool
+    {
+        return $this->action === self::ACTION_APPROVE;
+    }
+
+    /**
+     * 判断是否是拒绝操作
+     */
+    public function isRejected(): bool
+    {
+        return $this->action === self::ACTION_REJECT;
+    }
+}