📦 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/underscore/underscore-node.mjs

@@ -0,0 +1,7 @@
+//     Underscore.js 1.13.6
+//     https://underscorejs.org
+//     (c) 2009-2022 Jeremy Ashkenas, Julian Gonggrijp, and DocumentCloud and Investigative Reporters & Editors
+//     Underscore may be freely distributed under the MIT license.
+
+export { VERSION, after, every as all, allKeys, some as any, extendOwn as assign, before, bind, bindAll, chain, chunk, clone, map as collect, compact, compose, constant, contains, countBy, create, debounce, _ as default, defaults, defer, delay, find as detect, difference, rest as drop, each, _escape as escape, every, extend, extendOwn, filter, find, findIndex, findKey, findLastIndex, findWhere, first, flatten, reduce as foldl, reduceRight as foldr, each as forEach, functions, get, groupBy, has, first as head, identity, contains as include, contains as includes, indexBy, indexOf, initial, reduce as inject, intersection, invert, invoke, isArguments, isArray, isArrayBuffer, isBoolean, isDataView, isDate, isElement, isEmpty, isEqual, isError, isFinite, isFunction, isMap, isMatch, isNaN, isNull, isNumber, isObject, isRegExp, isSet, isString, isSymbol, isTypedArray, isUndefined, isWeakMap, isWeakSet, iteratee, keys, last, lastIndexOf, map, mapObject, matcher, matcher as matches, max, memoize, functions as methods, min, mixin, negate, noop, now, object, omit, once, pairs, partial, partition, pick, pluck, property, propertyOf, random, range, reduce, reduceRight, reject, rest, restArguments, result, sample, filter as select, shuffle, size, some, sortBy, sortedIndex, rest as tail, first as take, tap, template, templateSettings, throttle, times, toArray, toPath, unzip as transpose, _unescape as unescape, union, uniq, uniq as unique, uniqueId, unzip, values, where, without, wrap, zip } from './underscore-node-f.cjs';
+//# sourceMappingURL=underscore-node.mjs.map