refactor: 重构后端目录结构和命名规范

- 将后端目录名从大写改为小写 (Controller->controller 等)
- 将命名空间从 App\ 改为 app\ (符合 webman 官方规范)
- 移除不必要的 bootstrap 目录
- 完善出差审批业务功能：
  - 添加删除草稿功能
  - 添加审批操作功能（同意/拒绝）
  - 完善审批详情页，显示审批人和审批记录
- 前端优化：
  - 调整列表页行高
  - 隐藏底部导航栏
  - 仪表盘只显示3个快捷入口

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

backend/app/model/ApprovalOrder.php

@@ -0,0 +1,91 @@
+<?php
+
+namespace app\model;
+
+use Illuminate\Database\Eloquent\Model;
+
+class ApprovalOrder extends Model
+{
+    protected $table = 'approval_order';
+
+    protected $fillable = [
+        'business_type',
+        'business_id',
+        'title',
+        'applicant_id',
+        'status',
+        'current_nodes',
+        'flow_id',
+        'form_data',
+        'attachments',
+    ];
+
+    protected $casts = [
+        'current_nodes' => 'array',
+        'form_data' => 'array',
+        'attachments' => 'array',
+        'created_at' => 'datetime',
+        'updated_at' => 'datetime',
+    ];
+
+    /**
+     * 审批状态常量
+     */
+    const STATUS_DRAFT = 'draft';         // 草稿
+    const STATUS_PENDING = 'pending';     // 审批中
+    const STATUS_APPROVED = 'approved';   // 已通过
+    const STATUS_REJECTED = 'rejected';   // 已拒绝
+    const STATUS_CANCELLED = 'cancelled'; // 已撤销
+
+    /**
+     * 关联流程
+     */
+    public function flow()
+    {
+        return $this->belongsTo(ApprovalFlow::class, 'flow_id');
+    }
+
+    /**
+     * 关联申请人
+     */
+    public function applicant()
+    {
+        return $this->belongsTo(User::class, 'applicant_id');
+    }
+
+    /**
+     * 关联审批记录
+     */
+    public function records()
+    {
+        return $this->hasMany(ApprovalRecord::class, 'order_id')->orderBy('created_at');
+    }
+
+    /**
+     * 判断是否可以编辑
+     */
+    public function canEdit(): bool
+    {
+        return $this->status === self::STATUS_DRAFT;
+    }
+
+    /**
+     * 判断是否可以审批
+     */
+    public function canApprove(): bool
+    {
+        return $this->status === self::STATUS_PENDING;
+    }
+
+    /**
+     * 判断是否已结束
+     */
+    public function isEnded(): bool
+    {
+        return in_array($this->status, [
+            self::STATUS_APPROVED,
+            self::STATUS_REJECTED,
+            self::STATUS_CANCELLED,
+        ]);
+    }
+}