📦 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/duplexer/test/index.js

@@ -0,0 +1,31 @@
+var through = require("through")
+var test    = require("tape")
+
+var duplex  = require("../index")
+
+var readable = through()
+var writable = through(write)
+var written = 0
+var data = 0
+
+var stream = duplex(writable, readable)
+
+function write() {
+    written++
+}
+
+stream.on("data", ondata)
+
+function ondata() {
+    data++
+}
+
+test("emit and write", function(t) {
+    t.plan(2)
+
+    stream.write()
+    readable.emit("data")
+
+    t.equal(written, 1, "should have written once")
+    t.equal(data, 1, "should have received once")
+})