docs(editor): improve editor-app build documentation and add build:rapier2d script

- Add `pnpm build:rapier2d` command to automate Rapier2D WASM build process
- Fix gen-src.mjs path to correctly locate thirdparty/rapier.js
- Update init.ts to work with new wasm-pack web target (auto-initialization)
- Fix behavior-tree-editor build config for asset-system dependency
- Update README_CN.md and README.md with simplified build instructions

packages/editor/editor-app/README.md

@@ -8,12 +8,23 @@ Before running the editor, ensure you have the following installed:
 
 - **Node.js** >= 18.x
 - **pnpm** >= 10.x
-- **Rust** >= 1.70 (for Tauri)
+- **Rust** >= 1.70 (for Tauri and WASM builds)
+- **wasm-pack** (for building Rapier2D physics engine)
 - **Platform-specific dependencies**:
   - **Windows**: Microsoft Visual Studio C++ Build Tools
   - **macOS**: Xcode Command Line Tools (`xcode-select --install`)
   - **Linux**: See [Tauri prerequisites](https://tauri.app/v1/guides/getting-started/prerequisites)
 
+### Installing wasm-pack
+
+```bash
+# Using cargo
+cargo install wasm-pack
+
+# Or using the official installer script (Linux/macOS)
+curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | sh
+```
+
 ## Quick Start
 
 ### 1. Clone and Install
@@ -24,7 +35,23 @@ cd esengine
 pnpm install
 ```
 
-### 2. Build Dependencies
+### 2. Build Rapier2D WASM
+
+The editor depends on Rapier2D physics engine WASM artifacts. First-time setup only requires one command:
+
+```bash
+pnpm build:rapier2d
+```
+
+This command automatically:
+1. Prepares the Rust project
+2. Builds WASM
+3. Copies artifacts to `packages/physics/rapier2d/pkg`
+4. Generates TypeScript source code
+
+> **Note**: Requires Rust and wasm-pack to be installed.
+
+### 3. Build Editor
 
 From the project root:
 
@@ -32,7 +59,7 @@ From the project root:
 pnpm build:editor
 ```
 
-### 3. Run Editor
+### 4. Run Editor
 
 ```bash
 cd packages/editor/editor-app
@@ -43,6 +70,8 @@ pnpm tauri:dev
 
 | Script | Description |
 |--------|-------------|
+| `pnpm build:rapier2d` | Build Rapier2D WASM (required for first-time setup) |
+| `pnpm build:editor` | Build editor and all dependencies |
 | `pnpm tauri:dev` | Run editor in development mode with hot-reload |
 | `pnpm tauri:build` | Build production application |
 | `pnpm build:sdk` | Build editor-runtime SDK |
@@ -62,6 +91,17 @@ editor-app/
 
 ## Troubleshooting
 
+### Rapier2D WASM Build Failed
+
+**Error**: `Could not resolve "../pkg/rapier_wasm2d"`
+
+**Cause**: Missing Rapier2D WASM artifacts.
+
+**Solution**:
+1. Ensure `wasm-pack` is installed: `cargo install wasm-pack`
+2. Run `pnpm build:rapier2d`
+3. Verify `packages/physics/rapier2d/pkg/` directory exists and contains `rapier_wasm2d_bg.wasm` file
+
 ### Build Errors
 
 ```bash
@@ -76,6 +116,12 @@ pnpm build:editor
 rustup update
 ```
 
+### Windows Users Building WASM
+
+The `pnpm build:rapier2d` script works directly on Windows. If you encounter issues:
+1. Use Git Bash or WSL
+2. Or download pre-built WASM artifacts from [Releases](https://github.com/esengine/esengine/releases)
+
 ## Documentation
 
 - [ESEngine Documentation](https://esengine.cn/)