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/Controller/BusinessTripController.php

@@ -1,60 +0,0 @@
-<?php
-
-namespace App\Controller;
-
-use Webman\Http\Request;
-use Webman\Http\Response;
-
-class BusinessTripController extends BaseController
-{
-    /**
-     * 获取出差列表
-     */
-    public function list(Request $request): Response
-    {
-        $type = $request->input('type', 'my');
-
-        // TODO: 从数据库获取出差列表
-        return $this->success([
-            'list' => [],
-            'total' => 0,
-        ]);
-    }
-
-    /**
-     * 获取出差详情
-     */
-    public function detail(Request $request): Response
-    {
-        $id = $request->route('id');
-
-        // TODO: 从数据库获取出差详情
-        return $this->success([
-            'id' => $id,
-            'title' => '测试出差',
-        ]);
-    }
-
-    /**
-     * 提交出差申请
-     */
-    public function apply(Request $request): Response
-    {
-        $data = $request->all();
-
-        // TODO: 保存出差数据并创建审批流程
-        return $this->success();
-    }
-
-    /**
-     * 更新出差申请
-     */
-    public function update(Request $request): Response
-    {
-        $id = $request->route('id');
-        $data = $request->all();
-
-        // TODO: 更新出差数据
-        return $this->success();
-    }
-}