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

@@ -0,0 +1,62 @@
+<?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();
+    }
+}