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/ApprovalNode.php

@@ -1,79 +0,0 @@
-<?php
-
-namespace App\Model;
-
-use support\Model;
-
-class ApprovalNode extends Model
-{
-    protected $table = 'approval_node';
-
-    protected $fillable = [
-        'flow_id',
-        'type',
-        'name',
-        'order',
-        'approvers',
-        'conditions',
-    ];
-
-    protected $casts = [
-        'approvers' => 'array',
-        'conditions' => 'array',
-        'order' => 'integer',
-        'created_at' => 'datetime',
-        'updated_at' => 'datetime',
-    ];
-
-    /**
-     * 节点类型常量
-     */
-    const TYPE_APPROVER = 'approver';       // 审批人（单人）
-    const TYPE_AND_APPROVE = 'and_approve'; // 会签（需所有人通过）
-    const TYPE_OR_APPROVE = 'or_approve';   // 或签（任一人通过）
-    const TYPE_NOTIFY = 'notify';           // 抄送（通知用）
-
-    /**
-     * 关联流程
-     */
-    public function flow()
-    {
-        return $this->belongsTo(ApprovalFlow::class, 'flow_id');
-    }
-
-    /**
-     * 获取指定顺序的节点
-     */
-    public function scopeByOrder($query, int $order)
-    {
-        return $query->where('order', $order);
-    }
-
-    /**
-     * 判断是否是审批节点
-     */
-    public function isApprovalNode(): bool
-    {
-        return in_array($this->type, [
-            self::TYPE_APPROVER,
-            self::TYPE_AND_APPROVE,
-            self::TYPE_OR_APPROVE,
-        ]);
-    }
-
-    /**
-     * 判断是否是会签
-     */
-    public function isAndApprove(): bool
-    {
-        return $this->type === self::TYPE_AND_APPROVE;
-    }
-
-    /**
-     * 判断是否是或签
-     */
-    public function isOrApprove(): bool
-    {
-        return $this->type === self::TYPE_OR_APPROVE;
-    }
-}