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/UserController.php

@@ -1,62 +0,0 @@
-<?php
-
-namespace App\Controller;
-
-use Webman\Http\Request;
-use Webman\Http\Response;
-
-class UserController extends BaseController
-{
-    /**
-     * 获取用户信息
-     */
-    public function info(Request $request): Response
-    {
-        $userId = $this->getUserId($request);
-
-        // TODO: 从数据库获取用户信息
-        return $this->success([
-            'id' => $userId,
-            'name' => '测试用户',
-            'email' => 'test@example.com',
-            'company_id' => 1,
-        ]);
-    }
-
-    /**
-     * 获取用户菜单权限
-     */
-    public function menu(Request $request): Response
-    {
-        // TODO: 根据用户权限返回菜单
-        return $this->success([
-            ['id' => 1, 'name' => '首页', 'path' => '/dashboard'],
-            ['id' => 2, 'name' => '出差审批', 'path' => '/business-trip'],
-        ]);
-    }
-
-    /**
-     * 获取用户可切换的公司列表
-     */
-    public function companies(Request $request): Response
-    {
-        $userId = $this->getUserId($request);
-
-        // TODO: 从数据库获取用户关联的公司列表
-        return $this->success([
-            ['id' => 1, 'name' => '公司A'],
-        ]);
-    }
-
-    /**
-     * 切换当前公司
-     */
-    public function switchCompany(Request $request): Response
-    {
-        $companyId = $request->post('company_id');
-
-        // TODO: 更新用户当前公司
-
-        return $this->success();
-    }
-}