refactor: fix directory structure and namespaces for webman conventions

- Rename directories to lowercase: Controller→controller, Model→model, Service→service, Util→util, Bootstrap→bootstrap
- Update all namespaces from App\Xxx to app\xxx (webman convention)
- Update all import statements across the codebase
- Update route.php to use lowercase namespaces
- Remove unused CompanyFeishuApp model
- Comment out unimplemented controller routes

Following webman 2.x framework conventions:
- Models: app\model\{ClassName}
- Controllers: app\controller\{ClassName}
- Services: app\service\{ClassName}
- Utils: app\util\{ClassName}
- Middleware: app\middleware\{ClassName}

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

backend/app/Model/ApprovalRecord.php

@@ -1,63 +0,0 @@
-<?php
-
-namespace App\Model;
-
-use support\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;
-    }
-}