📦 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/cssstyle/lib/properties/borderSpacing.js

@@ -0,0 +1,41 @@
+'use strict';
+
+var parsers = require('../parsers');
+
+// <length> <length>? | inherit
+// if one, it applies to both horizontal and verical spacing
+// if two, the first applies to the horizontal and the second applies to vertical spacing
+
+var parse = function parse(v) {
+  if (v === '' || v === null) {
+    return undefined;
+  }
+  if (v === 0) {
+    return '0px';
+  }
+  if (v.toLowerCase() === 'inherit') {
+    return v;
+  }
+  var parts = v.split(/\s+/);
+  if (parts.length !== 1 && parts.length !== 2) {
+    return undefined;
+  }
+  parts.forEach(function(part) {
+    if (parsers.valueType(part) !== parsers.TYPES.LENGTH) {
+      return undefined;
+    }
+  });
+
+  return v;
+};
+
+module.exports.definition = {
+  set: function(v) {
+    this._setProperty('border-spacing', parse(v));
+  },
+  get: function() {
+    return this.getPropertyValue('border-spacing');
+  },
+  enumerable: true,
+  configurable: true,
+};