📦 添加虚拟环境和启动脚本

新增:
- backend/venv/ - Python 虚拟环境
- backend/start.sh - 启动脚本（使用虚拟环境）
- backend/requirements.txt - 依赖列表
- .gitignore - 忽略虚拟环境和缓存文件

说明:
- 每个项目使用独立虚拟环境
- 避免依赖冲突
- 启动脚本自动创建和激活虚拟环境

frontend/node_modules/source-map/lib/read-wasm-browser.js

@@ -0,0 +1,23 @@
+"use strict";
+
+let mappingsWasm = null;
+
+module.exports = function readWasm() {
+  if (typeof mappingsWasm === "string") {
+    return fetch(mappingsWasm).then(response => response.arrayBuffer());
+  }
+  if (mappingsWasm instanceof ArrayBuffer) {
+    return Promise.resolve(mappingsWasm);
+  }
+
+  throw new Error(
+    "You must provide the string URL or ArrayBuffer contents " +
+      "of lib/mappings.wasm by calling " +
+      "SourceMapConsumer.initialize({ 'lib/mappings.wasm': ... }) " +
+      "before using SourceMapConsumer"
+  );
+};
+
+module.exports.initialize = input => {
+  mappingsWasm = input;
+};