fix(ecs): resolve ESM require is not defined error (#402)

- Add RuntimeConfig module as standalone runtime environment storage
- Core.runtimeEnvironment and Scene.runtimeEnvironment now read from RuntimeConfig
- Remove require() call in Scene.ts to fix Node.js ESM compatibility

Fixes ReferenceError: require is not defined when using scene.isServer in ESM environment

packages/framework/core/src/RuntimeConfig.ts

@@ -0,0 +1,50 @@
+import type { RuntimeEnvironment } from './Types';
+
+/**
+ * @zh 全局运行时配置
+ * @en Global runtime configuration
+ *
+ * @zh 独立模块，避免 Core 和 Scene 之间的循环依赖
+ * @en Standalone module to avoid circular dependency between Core and Scene
+ */
+class RuntimeConfigClass {
+    private _runtimeEnvironment: RuntimeEnvironment = 'standalone';
+
+    /**
+     * @zh 获取运行时环境
+     * @en Get runtime environment
+     */
+    get runtimeEnvironment(): RuntimeEnvironment {
+        return this._runtimeEnvironment;
+    }
+
+    /**
+     * @zh 设置运行时环境
+     * @en Set runtime environment
+     */
+    set runtimeEnvironment(value: RuntimeEnvironment) {
+        this._runtimeEnvironment = value;
+    }
+
+    /**
+     * @zh 是否在服务端运行
+     * @en Whether running on server
+     */
+    get isServer(): boolean {
+        return this._runtimeEnvironment === 'server';
+    }
+
+    /**
+     * @zh 是否在客户端运行
+     * @en Whether running on client
+     */
+    get isClient(): boolean {
+        return this._runtimeEnvironment === 'client';
+    }
+}
+
+/**
+ * @zh 全局运行时配置单例
+ * @en Global runtime configuration singleton
+ */
+export const RuntimeConfig = new RuntimeConfigClass();