refactor(core): remove ManagerRegistry singleton, use instance-based DI

Replace static getInstance() pattern with public constructor to enable
multiple independent BimEngine instances on the same page. BaseManager
and BaseDialogManager now accept registry via constructor parameter.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/core/manager-registry.ts

@@ -1,6 +1,6 @@
 /**
  * Manager 注册表
- * 全局单例，提供所有 Manager 的集中访问点
+ * 每个 BimEngine 实例持有独立的 Registry，实现多实例隔离
  */
 import { EventEmitter } from './event-emitter';
 import type { EngineEvents } from '../types/events';
@@ -24,12 +24,10 @@ import type { ComponentDetailManager } from '../managers/component-detail-manage
 import type { AiChatManager } from '../managers/ai-chat-manager';
 
 /**
- * Manager 注册表 - 单例模式
- * 提供所有 Manager 的全局访问点,替代 engine 层层传递
+ * Manager 注册表 - 实例模式
+ * 每个 BimEngine 创建独立的 Registry 实例，替代旧的全局单例
  */
 export class ManagerRegistry {
-    /** 单例实例 */
-    private static instance: ManagerRegistry | null = null;
     /** 事件发射器 */
     private eventEmitter: EventEmitter = new EventEmitter();
 
@@ -72,22 +70,29 @@ export class ManagerRegistry {
     /** AI 聊天管理器 */
     public aiChat: AiChatManager | null = null;
 
-    private constructor() {}
+    constructor() {}
 
-    /** 获取单例实例 */
-    public static getInstance(): ManagerRegistry {
-        if (!ManagerRegistry.instance) {
-            ManagerRegistry.instance = new ManagerRegistry();
-        }
-        return ManagerRegistry.instance;
-    }
-
-    /** 重置单例（用于测试或重新初始化） */
-    public static reset(): void {
-        if (ManagerRegistry.instance) {
-            ManagerRegistry.instance.eventEmitter.clear();
-            ManagerRegistry.instance = null;
-        }
+    /** 重置（清理事件和引用） */
+    public reset(): void {
+        this.eventEmitter.clear();
+        this.container = null;
+        this.wrapper = null;
+        this.toolbar = null;
+        this.dialog = null;
+        this.engine3d = null;
+        this.buttonGroup = null;
+        this.rightKey = null;
+        this.constructTree = null;
+        this.measure = null;
+        this.walkControl = null;
+        this.sectionPlane = null;
+        this.sectionAxis = null;
+        this.sectionBox = null;
+        this.walkPath = null;
+        this.walkPlanView = null;
+        this.engineInfo = null;
+        this.componentDetail = null;
+        this.aiChat = null;
     }
 
     /**