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/util/Db.php

@@ -0,0 +1,66 @@
+<?php
+
+namespace app\util;
+
+use Illuminate\Database\Capsule\Manager as Capsule;
+use Illuminate\Events\Dispatcher;
+use Illuminate\Container\Container;
+use Illuminate\Database\Eloquent\Model as EloquentModel;
+
+class Db
+{
+    private static ?Capsule $capsule = null;
+
+    public static function init(): void
+    {
+        if (self::$capsule !== null) {
+            return;
+        }
+
+        $config = config('database');
+
+        self::$capsule = new Capsule();
+
+        // Add connection
+        self::$capsule->addConnection([
+            'driver' => 'mysql',
+            'host' => getenv('DB_HOST') ?: '127.0.0.1',
+            'port' => getenv('DB_PORT') ?: '3306',
+            'database' => getenv('DB_DATABASE') ?: 'x_server_mobile',
+            'username' => getenv('DB_USERNAME') ?: 'root',
+            'password' => getenv('DB_PASSWORD') ?: '',
+            'charset' => 'utf8mb4',
+            'collation' => 'utf8mb4_unicode_ci',
+            'prefix' => '',
+            'strict' => true,
+            'engine' => null,
+        ]);
+
+        // Set event dispatcher
+        self::$capsule->setEventDispatcher(new Dispatcher(new Container()));
+
+        // Make this Capsule instance available globally via static methods
+        self::$capsule->setAsGlobal();
+
+        // Setup the Eloquent ORM
+        self::$capsule->bootEloquent();
+    }
+
+    public static function connection(?string $name = null): \Illuminate\Database\Connection
+    {
+        if (self::$capsule === null) {
+            self::init();
+        }
+        return self::$capsule->connection($name);
+    }
+
+    public static function table(string $table): \Illuminate\Database\Query\Builder
+    {
+        return self::connection()->table($table);
+    }
+
+    public static function raw(string $value): \Illuminate\Database\Query\Expression
+    {
+        return self::connection()->raw($value);
+    }
+}