📦 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/tailwindcss/scripts/release-channel.js

@@ -0,0 +1,18 @@
+// Given a version, figure out what the release channel is so that we can publish to the correct
+// channel on npm.
+//
+// E.g.:
+//
+//   1.2.3                  -> latest (default)
+//   0.0.0-insiders.ffaa88  -> insiders
+//   4.1.0-alpha.4          -> alpha
+
+let version =
+  process.argv[2] || process.env.npm_package_version || require('../package.json').version
+
+let match = /\d+\.\d+\.\d+-(.*)\.\d+/g.exec(version)
+if (match) {
+  console.log(match[1])
+} else {
+  console.log('latest')
+}