feat(platform-web): 添加BrowserRuntime和资产读取

packages/platform-web/src/index.ts

@@ -1,29 +1,69 @@
 /**
  * @esengine/platform-web
  *
- * Web/H5 平台适配器 - 仅包含平台差异代码
- * 通用运行时逻辑在 @esengine/runtime-core
+ * Web/H5 Platform Adapter
+ * Web/H5 平台适配器
+ *
+ * Provides browser-specific implementations:
+ * - BrowserRuntime: Main entry point for game builds
+ * - BrowserAssetReader: Asset loading via fetch API
+ * - Web subsystems: Canvas, Input, Storage, WASM
  *
  * @packageDocumentation
  */
 
-// Web 平台子系统
+// ============================================
+// Runtime (main entry for game builds)
+// ============================================
+export {
+    BrowserRuntime,
+    create,
+    type RuntimeConfig
+} from './BrowserRuntime';
+
+// Default export for convenient usage in game builds
+export { default } from './BrowserRuntime';
+
+// Asset reader
+export { BrowserAssetReader } from './BrowserAssetReader';
+
+// ============================================
+// Web Platform Subsystems
+// ============================================
 export { WebCanvasSubsystem } from './subsystems/WebCanvasSubsystem';
 export { WebInputSubsystem } from './subsystems/WebInputSubsystem';
 export { WebStorageSubsystem } from './subsystems/WebStorageSubsystem';
 export { WebWASMSubsystem } from './subsystems/WebWASMSubsystem';
 
-// Web 特定系统
+// ============================================
+// Web-specific Systems
+// ============================================
 export { Canvas2DRenderSystem } from './systems/Canvas2DRenderSystem';
 
+// ============================================
+// Platform Detection Utilities
+// ============================================
+
+/**
+ * Check if running in web browser
+ * 检查是否在浏览器中运行
+ */
 export function isWebPlatform(): boolean {
     return typeof window !== 'undefined' && typeof document !== 'undefined';
 }
 
+/**
+ * Get canvas element by ID
+ * 根据 ID 获取 canvas 元素
+ */
 export function getWebCanvas(canvasId: string): HTMLCanvasElement | null {
     return document.getElementById(canvasId) as HTMLCanvasElement | null;
 }
 
+/**
+ * Create a new canvas element
+ * 创建新的 canvas 元素
+ */
 export function createWebCanvas(width: number, height: number): HTMLCanvasElement {
     const canvas = document.createElement('canvas');
     canvas.width = width;