📦 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/postcss-normalize-unicode/LICENSE-MIT

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+Copyright (c) Ben Briggs <beneb.info@gmail.com> (http://beneb.info)
+
+Permission is hereby granted, free of charge, to any person
+obtaining a copy of this software and associated documentation
+files (the "Software"), to deal in the Software without
+restriction, including without limitation the rights to use,
+copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the
+Software is furnished to do so, subject to the following
+conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+OTHER DEALINGS IN THE SOFTWARE.

frontend/node_modules/postcss-normalize-unicode/README.md

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+# [postcss][postcss]-normalize-unicode
+
+> Normalize unicode with PostCSS.
+
+## Install
+
+With [npm](https://npmjs.org/package/postcss-normalize-unicode) do:
+
+```
+npm install postcss-normalize-unicode --save
+```
+
+## Example
+
+### Input
+
+```css
+@font-face{
+    font-family: test;
+    unicode-range: u+2b00-2bff
+}
+```
+
+### Output
+
+```css
+@font-face{
+    font-family: test;
+    unicode-range: u+2b??
+}
+``` 
+
+## Usage
+
+See the [PostCSS documentation](https://github.com/postcss/postcss#usage) for
+examples for your environment.
+
+## Contributors
+
+See [CONTRIBUTORS.md](https://github.com/cssnano/cssnano/blob/master/CONTRIBUTORS.md).
+
+## License
+
+MIT © [Ben Briggs](http://beneb.info)
+
+[postcss]: https://github.com/postcss/postcss

frontend/node_modules/postcss-normalize-unicode/package.json

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+{
+  "name": "postcss-normalize-unicode",
+  "version": "5.1.1",
+  "description": "Normalize unicode-range descriptors, and can convert to wildcard ranges.",
+  "main": "src/index.js",
+  "types": "types/index.d.ts",
+  "files": [
+    "src",
+    "LICENSE-MIT",
+    "types"
+  ],
+  "keywords": [
+    "css",
+    "postcss",
+    "postcss-plugin"
+  ],
+  "license": "MIT",
+  "homepage": "https://github.com/cssnano/cssnano",
+  "author": {
+    "name": "Ben Briggs",
+    "email": "beneb.info@gmail.com",
+    "url": "http://beneb.info"
+  },
+  "repository": "cssnano/cssnano",
+  "dependencies": {
+    "browserslist": "^4.21.4",
+    "postcss-value-parser": "^4.2.0"
+  },
+  "bugs": {
+    "url": "https://github.com/cssnano/cssnano/issues"
+  },
+  "engines": {
+    "node": "^10 || ^12 || >=14.0"
+  },
+  "devDependencies": {
+    "postcss": "^8.2.15"
+  },
+  "peerDependencies": {
+    "postcss": "^8.2.15"
+  }
+}

frontend/node_modules/postcss-normalize-unicode/src/index.js

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+'use strict';
+const browserslist = require('browserslist');
+const valueParser = require('postcss-value-parser');
+
+const regexLowerCaseUPrefix = /^u(?=\+)/;
+
+/**
+ * @param {string} range
+ * @return {string}
+ */
+function unicode(range) {
+  const values = range.slice(2).split('-');
+
+  if (values.length < 2) {
+    return range;
+  }
+
+  const left = values[0].split('');
+  const right = values[1].split('');
+
+  if (left.length !== right.length) {
+    return range;
+  }
+
+  const merged = mergeRangeBounds(left, right);
+
+  if (merged) {
+    return merged;
+  }
+
+  return range;
+}
+/**
+ * @param {string[]} left
+ * @param {string[]} right
+ * @return {false|string}
+ */
+function mergeRangeBounds(left, right) {
+  let questionCounter = 0;
+  let group = 'u+';
+  for (const [index, value] of left.entries()) {
+    if (value === right[index] && questionCounter === 0) {
+      group = group + value;
+    } else if (value === '0' && right[index] === 'f') {
+      questionCounter++;
+      group = group + '?';
+    } else {
+      return false;
+    }
+  }
+  // The maximum number of wildcard characters (?) for ranges is 5.
+  if (questionCounter < 6) {
+    return group;
+  } else {
+    return false;
+  }
+}
+
+/**
+ * IE and Edge before 16 version ignore the unicode-range if the 'U' is lowercase
+ *
+ * https://caniuse.com/#search=unicode-range
+ *
+ * @param {string} browser
+ * @return {boolean}
+ */
+function hasLowerCaseUPrefixBug(browser) {
+  return browserslist('ie <=11, edge <= 15').includes(browser);
+}
+
+/**
+ * @param {string} value
+ * @return {string}
+ */
+function transform(value, isLegacy = false) {
+  return valueParser(value)
+    .walk((child) => {
+      if (child.type === 'unicode-range') {
+        const transformed = unicode(child.value.toLowerCase());
+
+        child.value = isLegacy
+          ? transformed.replace(regexLowerCaseUPrefix, 'U')
+          : transformed;
+      }
+
+      return false;
+    })
+    .toString();
+}
+
+/**
+ * @type {import('postcss').PluginCreator<void>}
+ * @return {import('postcss').Plugin}
+ */
+function pluginCreator() {
+  return {
+    postcssPlugin: 'postcss-normalize-unicode',
+    /** @param {import('postcss').Result & {opts: browserslist.Options}} result*/
+    prepare(result) {
+      const cache = new Map();
+      const resultOpts = result.opts || {};
+      const browsers = browserslist(null, {
+        stats: resultOpts.stats,
+        path: __dirname,
+        env: resultOpts.env,
+      });
+      const isLegacy = browsers.some(hasLowerCaseUPrefixBug);
+
+      return {
+        OnceExit(css) {
+          css.walkDecls(/^unicode-range$/i, (decl) => {
+            const value = decl.value;
+
+            if (cache.has(value)) {
+              decl.value = cache.get(value);
+
+              return;
+            }
+
+            const newValue = transform(value, isLegacy);
+
+            decl.value = newValue;
+            cache.set(value, newValue);
+          });
+        },
+      };
+    },
+  };
+}
+
+pluginCreator.postcss = true;
+module.exports = pluginCreator;

frontend/node_modules/postcss-normalize-unicode/types/index.d.ts

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+export = pluginCreator;
+/**
+ * @type {import('postcss').PluginCreator<void>}
+ * @return {import('postcss').Plugin}
+ */
+declare function pluginCreator(): import('postcss').Plugin;
+declare namespace pluginCreator {
+    const postcss: true;
+}