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/BaseController.php

@@ -0,0 +1,41 @@
+<?php
+
+namespace app\controller;
+
+use Webman\Http\Request;
+use Webman\Http\Response;
+
+abstract class BaseController
+{
+    /**
+     * 成功响应
+     */
+    protected function success($data = null, string $message = 'success'): Response
+    {
+        return json([
+            'code' => 0,
+            'message' => $message,
+            'data' => $data,
+        ]);
+    }
+
+    /**
+     * 错误响应
+     */
+    protected function error(string $message = 'error', int $code = 1, $data = null): Response
+    {
+        return json([
+            'code' => $code,
+            'message' => $message,
+            'data' => $data,
+        ]);
+    }
+
+    /**
+     * 获取当前用户ID
+     */
+    protected function getUserId(Request $request): ?int
+    {
+        return $request->userId ?? null;
+    }
+}