feat(behavior-tree): add pure BehaviorTreePlugin for Cocos/Laya integration (#400)

- Add BehaviorTreePlugin class that only depends on @esengine/ecs-framework
- Implement IPlugin interface with install(), uninstall(), setupScene() methods
- Remove esengine/ subdirectory that incorrectly depended on engine-core
- Update package documentation with correct usage examples

packages/framework/behavior-tree/src/BehaviorTreePlugin.ts

@@ -0,0 +1,118 @@
+import type { Core, ServiceContainer, IPlugin, IScene } from '@esengine/ecs-framework';
+import { BehaviorTreeExecutionSystem } from './execution/BehaviorTreeExecutionSystem';
+import { BehaviorTreeAssetManager } from './execution/BehaviorTreeAssetManager';
+import { GlobalBlackboardService } from './Services/GlobalBlackboardService';
+
+/**
+ * @zh 行为树插件
+ * @en Behavior Tree Plugin
+ *
+ * @zh 为 ECS 框架提供行为树支持的插件。
+ * 可与任何基于 @esengine/ecs-framework 的引擎集成（Cocos、Laya、Node.js 等）。
+ *
+ * @en Plugin that provides behavior tree support for ECS framework.
+ * Can be integrated with any engine based on @esengine/ecs-framework (Cocos, Laya, Node.js, etc.).
+ *
+ * @example
+ * ```typescript
+ * import { Core, Scene } from '@esengine/ecs-framework';
+ * import { BehaviorTreePlugin, BehaviorTreeBuilder, BehaviorTreeStarter } from '@esengine/behavior-tree';
+ *
+ * // Initialize
+ * Core.create();
+ * const plugin = new BehaviorTreePlugin();
+ * await Core.installPlugin(plugin);
+ *
+ * // Setup scene
+ * const scene = new Scene();
+ * plugin.setupScene(scene);
+ * Core.setScene(scene);
+ *
+ * // Create and start behavior tree
+ * const tree = BehaviorTreeBuilder.create('MyAI')
+ *     .selector('Root')
+ *         .log('Hello from behavior tree!')
+ *     .end()
+ *     .build();
+ *
+ * const entity = scene.createEntity('AIEntity');
+ * BehaviorTreeStarter.start(entity, tree);
+ * ```
+ */
+export class BehaviorTreePlugin implements IPlugin {
+    /**
+     * @zh 插件名称
+     * @en Plugin name
+     */
+    readonly name = '@esengine/behavior-tree';
+
+    /**
+     * @zh 插件版本
+     * @en Plugin version
+     */
+    readonly version = '1.0.0';
+
+    /**
+     * @zh 插件依赖
+     * @en Plugin dependencies
+     */
+    readonly dependencies: readonly string[] = [];
+
+    private _services: ServiceContainer | null = null;
+
+    /**
+     * @zh 安装插件
+     * @en Install plugin
+     *
+     * @param _core - Core 实例
+     * @param services - 服务容器
+     */
+    install(_core: Core, services: ServiceContainer): void {
+        this._services = services;
+
+        // Register services
+        if (!services.isRegistered(GlobalBlackboardService)) {
+            services.registerSingleton(GlobalBlackboardService);
+        }
+        if (!services.isRegistered(BehaviorTreeAssetManager)) {
+            services.registerSingleton(BehaviorTreeAssetManager);
+        }
+    }
+
+    /**
+     * @zh 卸载插件
+     * @en Uninstall plugin
+     */
+    uninstall(): void {
+        if (this._services) {
+            const assetManager = this._services.tryResolve(BehaviorTreeAssetManager);
+            if (assetManager) {
+                assetManager.dispose();
+            }
+
+            const blackboardService = this._services.tryResolve(GlobalBlackboardService);
+            if (blackboardService) {
+                blackboardService.dispose();
+            }
+        }
+        this._services = null;
+    }
+
+    /**
+     * @zh 设置场景，添加行为树执行系统
+     * @en Setup scene, add behavior tree execution system
+     *
+     * @param scene - 要设置的场景
+     *
+     * @example
+     * ```typescript
+     * const scene = new Scene();
+     * plugin.setupScene(scene);
+     * Core.setScene(scene);
+     * ```
+     */
+    setupScene(scene: IScene): void {
+        const system = new BehaviorTreeExecutionSystem(this._services ?? undefined);
+        scene.addSystem(system);
+    }
+}