📦 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/utils/colorSpace.js

@@ -0,0 +1,21 @@
+'use strict';
+
+const hueToRgb = (t1, t2, hue) => {
+  if (hue < 0) hue += 6;
+  if (hue >= 6) hue -= 6;
+
+  if (hue < 1) return (t2 - t1) * hue + t1;
+  else if (hue < 3) return t2;
+  else if (hue < 4) return (t2 - t1) * (4 - hue) + t1;
+  else return t1;
+};
+
+// https://www.w3.org/TR/css-color-4/#hsl-to-rgb
+exports.hslToRgb = (hue, sat, light) => {
+  const t2 = light <= 0.5 ? light * (sat + 1) : light + sat - light * sat;
+  const t1 = light * 2 - t2;
+  const r = hueToRgb(t1, t2, hue + 2);
+  const g = hueToRgb(t1, t2, hue);
+  const b = hueToRgb(t1, t2, hue - 2);
+  return [Math.round(r * 255), Math.round(g * 255), Math.round(b * 255)];
+};

frontend/node_modules/cssstyle/lib/utils/getBasicPropertyDescriptor.js

@@ -0,0 +1,14 @@
+'use strict';
+
+module.exports = function getBasicPropertyDescriptor(name) {
+  return {
+    set: function(v) {
+      this._setProperty(name, v);
+    },
+    get: function() {
+      return this.getPropertyValue(name);
+    },
+    enumerable: true,
+    configurable: true,
+  };
+};