📦 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/stylehacks/src/plugins/leadingStar.js

@@ -0,0 +1,55 @@
+'use strict';
+const BasePlugin = require('../plugin');
+const { IE_5_5, IE_6, IE_7 } = require('../dictionary/browsers');
+const { PROPERTY } = require('../dictionary/identifiers');
+const { ATRULE, DECL } = require('../dictionary/postcss');
+
+const hacks = '!_$_&_*_)_=_%_+_,_._/_`_]_#_~_?_:_|'.split('_');
+
+module.exports = class LeadingStar extends BasePlugin {
+  /** @param {import('postcss').Result=} result */
+  constructor(result) {
+    super([IE_5_5, IE_6, IE_7], [ATRULE, DECL], result);
+  }
+
+  /**
+   * @param {import('postcss').Declaration | import('postcss').AtRule} node
+   * @return {void}
+   */
+  detect(node) {
+    if (node.type === DECL) {
+      // some values are not picked up by before, so ensure they are
+      // at the beginning of the value
+      hacks.forEach((hack) => {
+        if (!node.prop.indexOf(hack)) {
+          this.push(node, {
+            identifier: PROPERTY,
+            hack: node.prop,
+          });
+        }
+      });
+      const { before } = node.raws;
+      if (!before) {
+        return;
+      }
+      hacks.forEach((hack) => {
+        if (before.includes(hack)) {
+          this.push(node, {
+            identifier: PROPERTY,
+            hack: `${before.trim()}${node.prop}`,
+          });
+        }
+      });
+    } else {
+      // test for the @property: value; hack
+      const { name } = node;
+      const len = name.length - 1;
+      if (name.lastIndexOf(':') === len) {
+        this.push(node, {
+          identifier: PROPERTY,
+          hack: `@${name.substr(0, len)}`,
+        });
+      }
+    }
+  }
+};