📦 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/connect-history-api-fallback/lib/index.js

@@ -0,0 +1,121 @@
+'use strict';
+
+var url = require('url');
+
+exports = module.exports = function historyApiFallback(options) {
+  options = options || {};
+  var logger = getLogger(options);
+
+  return function(req, res, next) {
+    var headers = req.headers;
+    if (req.method !== 'GET' && req.method !== 'HEAD') {
+      logger(
+        'Not rewriting',
+        req.method,
+        req.url,
+        'because the method is not GET or HEAD.'
+      );
+      return next();
+    } else if (!headers || typeof headers.accept !== 'string') {
+      logger(
+        'Not rewriting',
+        req.method,
+        req.url,
+        'because the client did not send an HTTP accept header.'
+      );
+      return next();
+    } else if (headers.accept.indexOf('application/json') === 0) {
+      logger(
+        'Not rewriting',
+        req.method,
+        req.url,
+        'because the client prefers JSON.'
+      );
+      return next();
+    } else if (!acceptsHtml(headers.accept, options)) {
+      logger(
+        'Not rewriting',
+        req.method,
+        req.url,
+        'because the client does not accept HTML.'
+      );
+      return next();
+    }
+
+    var parsedUrl = url.parse(req.url);
+    var rewriteTarget;
+    options.rewrites = options.rewrites || [];
+    for (var i = 0; i < options.rewrites.length; i++) {
+      var rewrite = options.rewrites[i];
+      var match = parsedUrl.pathname.match(rewrite.from);
+      if (match !== null) {
+        rewriteTarget = evaluateRewriteRule(parsedUrl, match, rewrite.to, req);
+
+        if(rewriteTarget.charAt(0) !== '/') {
+          logger(
+            'We recommend using an absolute path for the rewrite target.',
+            'Received a non-absolute rewrite target',
+            rewriteTarget,
+            'for URL',
+            req.url
+          );
+        }
+
+        logger('Rewriting', req.method, req.url, 'to', rewriteTarget);
+        req.url = rewriteTarget;
+        return next();
+      }
+    }
+
+    var pathname = parsedUrl.pathname;
+    if (pathname.lastIndexOf('.') > pathname.lastIndexOf('/') &&
+        options.disableDotRule !== true) {
+      logger(
+        'Not rewriting',
+        req.method,
+        req.url,
+        'because the path includes a dot (.) character.'
+      );
+      return next();
+    }
+
+    rewriteTarget = options.index || '/index.html';
+    logger('Rewriting', req.method, req.url, 'to', rewriteTarget);
+    req.url = rewriteTarget;
+    next();
+  };
+};
+
+function evaluateRewriteRule(parsedUrl, match, rule, req) {
+  if (typeof rule === 'string') {
+    return rule;
+  } else if (typeof rule !== 'function') {
+    throw new Error('Rewrite rule can only be of type string or function.');
+  }
+
+  return rule({
+    parsedUrl: parsedUrl,
+    match: match,
+    request: req
+  });
+}
+
+function acceptsHtml(header, options) {
+  options.htmlAcceptHeaders = options.htmlAcceptHeaders || ['text/html', '*/*'];
+  for (var i = 0; i < options.htmlAcceptHeaders.length; i++) {
+    if (header.indexOf(options.htmlAcceptHeaders[i]) !== -1) {
+      return true;
+    }
+  }
+  return false;
+}
+
+function getLogger(options) {
+  if (options && options.logger) {
+    return options.logger;
+  } else if (options && options.verbose) {
+    // eslint-disable-next-line no-console
+    return console.log.bind(console);
+  }
+  return function(){};
+}