📦 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/cssnano/src/index.js

@@ -0,0 +1,171 @@
+'use strict';
+const path = require('path');
+/** @type {any} */
+const postcss = require('postcss');
+const yaml = require('yaml');
+const { lilconfigSync } = require('lilconfig');
+
+const cssnano = 'cssnano';
+
+/** @typedef {{preset?: any, plugins?: any[], configFile?: string}} Options */
+/**
+ * @param {string} moduleId
+ * @returns {boolean}
+ */
+function isResolvable(moduleId) {
+  try {
+    require.resolve(moduleId);
+    return true;
+  } catch (e) {
+    return false;
+  }
+}
+
+/**
+ * preset can be one of four possibilities:
+ * preset = 'default'
+ * preset = ['default', {}]
+ * preset = function <- to be invoked
+ * preset = {plugins: []} <- already invoked function
+ *
+ * @param {any} preset
+ * @return {[import('postcss').PluginCreator<any>, boolean | Record<string, any> | undefined][]}}
+ */
+function resolvePreset(preset) {
+  let fn, options;
+
+  if (Array.isArray(preset)) {
+    fn = preset[0];
+    options = preset[1];
+  } else {
+    fn = preset;
+    options = {};
+  }
+
+  // For JS setups where we invoked the preset already
+  if (preset.plugins) {
+    return preset.plugins;
+  }
+
+  // Provide an alias for the default preset, as it is built-in.
+  if (fn === 'default') {
+    return require('cssnano-preset-default')(options).plugins;
+  }
+
+  // For non-JS setups; we'll need to invoke the preset ourselves.
+  if (typeof fn === 'function') {
+    return fn(options).plugins;
+  }
+
+  // Try loading a preset from node_modules
+  if (isResolvable(fn)) {
+    return require(fn)(options).plugins;
+  }
+
+  const sugar = `cssnano-preset-${fn}`;
+
+  // Try loading a preset from node_modules (sugar)
+  if (isResolvable(sugar)) {
+    return require(sugar)(options).plugins;
+  }
+
+  // If all else fails, we probably have a typo in the config somewhere
+  throw new Error(
+    `Cannot load preset "${fn}". Please check your configuration for errors and try again.`
+  );
+}
+
+/**
+ * cssnano will look for configuration firstly as options passed
+ * directly to it, and failing this it will use lilconfig to
+ * load an external file.
+
+ * @param {Options} options
+ */
+function resolveConfig(options) {
+  if (options.preset) {
+    return resolvePreset(options.preset);
+  }
+
+  /** @type {string | undefined} */
+  let searchPath = process.cwd();
+  let configPath = undefined;
+
+  if (options.configFile) {
+    searchPath = undefined;
+    configPath = path.resolve(process.cwd(), options.configFile);
+  }
+
+  const configExplorer = lilconfigSync(cssnano, {
+    searchPlaces: [
+      'package.json',
+      '.cssnanorc',
+      '.cssnanorc.json',
+      '.cssnanorc.yaml',
+      '.cssnanorc.yml',
+      '.cssnanorc.js',
+      'cssnano.config.js',
+    ],
+    loaders: {
+      '.yaml': (filepath, content) => yaml.parse(content),
+      '.yml': (filepath, content) => yaml.parse(content),
+    },
+  });
+  const config = configPath
+    ? configExplorer.load(configPath)
+    : configExplorer.search(searchPath);
+
+  if (config === null) {
+    return resolvePreset('default');
+  }
+
+  return resolvePreset(config.config.preset || config.config);
+}
+
+/**
+ * @type {import('postcss').PluginCreator<Options>}
+ * @param {Options=} options
+ * @return {import('postcss').Processor}
+ */
+function cssnanoPlugin(options = {}) {
+  if (Array.isArray(options.plugins)) {
+    if (!options.preset || !options.preset.plugins) {
+      options.preset = { plugins: [] };
+    }
+
+    options.plugins.forEach((plugin) => {
+      if (Array.isArray(plugin)) {
+        const [pluginDef, opts = {}] = plugin;
+        if (typeof pluginDef === 'string' && isResolvable(pluginDef)) {
+          options.preset.plugins.push([require(pluginDef), opts]);
+        } else {
+          options.preset.plugins.push([pluginDef, opts]);
+        }
+      } else if (typeof plugin === 'string' && isResolvable(plugin)) {
+        options.preset.plugins.push([require(plugin), {}]);
+      } else {
+        options.preset.plugins.push([plugin, {}]);
+      }
+    });
+  }
+  const plugins = [];
+  const nanoPlugins = resolveConfig(options);
+  for (const nanoPlugin of nanoPlugins) {
+    if (Array.isArray(nanoPlugin)) {
+      const [processor, opts] = nanoPlugin;
+      if (
+        typeof opts === 'undefined' ||
+        (typeof opts === 'object' && !opts.exclude) ||
+        (typeof opts === 'boolean' && opts === true)
+      ) {
+        plugins.push(processor(opts));
+      }
+    } else {
+      plugins.push(nanoPlugin);
+    }
+  }
+  return postcss(plugins);
+}
+
+cssnanoPlugin.postcss = true;
+module.exports = cssnanoPlugin;