📦 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/sucrase/bin/sucrase

@@ -0,0 +1,3 @@
+#!/usr/bin/env node
+
+require("../dist/cli").default();

frontend/node_modules/sucrase/bin/sucrase-node

@@ -0,0 +1,18 @@
+#!/usr/bin/env node
+const Module = require("module");
+const {resolve} = require("path");
+
+/*
+ * Simple wrapper around node that first registers Sucrase with default settings.
+ *
+ * This is meant for simple use cases, and doesn't support custom Node/V8 args,
+ * executing a code snippet, a REPL, or other things that you might find in
+ * node, babel-node, or ts-node. For more advanced use cases, you can use
+ * `node -r sucrase/register` or register a require hook programmatically from
+ * your own code.
+ */
+require("../register");
+
+process.argv.splice(1, 1);
+process.argv[1] = resolve(process.argv[1]);
+Module.runMain();