docs(code): add JSDoc comments for clipping API methods

Add comprehensive documentation for:
- activeSection(mode): Unified activation API with mode descriptions
- getCurrentSectionMode(): Current mode getter
- setSectionBoxRange(range): Box range setter with percentage format
- deactivateSection(): Unified deactivation

Includes @param, @returns, @remarks, and @example sections in Chinese.

src/managers/engine-manager.ts

@@ -255,8 +255,9 @@ export class EngineManager extends BaseManager {
     }
 
     /**
-     * 激活轴向剖切
-     * @param axis 要激活的轴向 ('x' | 'y' | 'z')
+     * 激活剖切功能（统一入口）
+     * @param mode 剖切模式: 'x' | 'y' | 'z' (轴向剖切) | 'box' (剖切盒) | 'face' (拾取面剖切)
+     * @remarks 代理调用 Engine.activeSection(mode)
      */
     public activeSection(mode: 'x' | 'y' | 'z' | 'box' | 'face'): void {
         if (!this.engineInstance) {
@@ -266,6 +267,10 @@ export class EngineManager extends BaseManager {
         this.engineInstance.activeSection(mode);
     }
 
+    /**
+     * 获取当前激活的剖切模式
+     * @returns 当前剖切模式，未激活时返回 null
+     */
     public getCurrentSectionMode(): 'x' | 'y' | 'z' | 'box' | 'face' | null {
         if (!this.engineInstance) {
             return null;
@@ -273,6 +278,10 @@ export class EngineManager extends BaseManager {
         return this.engineInstance.getCurrentSectionMode();
     }
 
+    /**
+     * 停用所有剖切功能
+     * @remarks 关闭剖切对话框时调用
+     */
     public deactivateSection(): void {
         if (!this.engineInstance) {
             return;
@@ -280,6 +289,11 @@ export class EngineManager extends BaseManager {
         this.engineInstance.deactivateSection();
     }
 
+    /**
+     * 设置剖切盒范围
+     * @param range 各轴的剖切范围 (百分比 0-100)
+     * @remarks 仅在 'box' 模式下有效
+     */
     public setSectionBoxRange(range: SectionBoxRange): void {
         if (!this.engineInstance) {
             console.warn('[EngineManager] 3D Engine not initialized.');