📦 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/fs-extra/lib/json/index.js

@@ -0,0 +1,16 @@
+'use strict'
+
+const u = require('universalify').fromPromise
+const jsonFile = require('./jsonfile')
+
+jsonFile.outputJson = u(require('./output-json'))
+jsonFile.outputJsonSync = require('./output-json-sync')
+// aliases
+jsonFile.outputJSON = jsonFile.outputJson
+jsonFile.outputJSONSync = jsonFile.outputJsonSync
+jsonFile.writeJSON = jsonFile.writeJson
+jsonFile.writeJSONSync = jsonFile.writeJsonSync
+jsonFile.readJSON = jsonFile.readJson
+jsonFile.readJSONSync = jsonFile.readJsonSync
+
+module.exports = jsonFile

frontend/node_modules/fs-extra/lib/json/jsonfile.js

@@ -0,0 +1,11 @@
+'use strict'
+
+const jsonFile = require('jsonfile')
+
+module.exports = {
+  // jsonfile exports
+  readJson: jsonFile.readFile,
+  readJsonSync: jsonFile.readFileSync,
+  writeJson: jsonFile.writeFile,
+  writeJsonSync: jsonFile.writeFileSync
+}

frontend/node_modules/fs-extra/lib/json/output-json-sync.js

@@ -0,0 +1,12 @@
+'use strict'
+
+const { stringify } = require('jsonfile/utils')
+const { outputFileSync } = require('../output-file')
+
+function outputJsonSync (file, data, options) {
+  const str = stringify(data, options)
+
+  outputFileSync(file, str, options)
+}
+
+module.exports = outputJsonSync

frontend/node_modules/fs-extra/lib/json/output-json.js

@@ -0,0 +1,12 @@
+'use strict'
+
+const { stringify } = require('jsonfile/utils')
+const { outputFile } = require('../output-file')
+
+async function outputJson (file, data, options = {}) {
+  const str = stringify(data, options)
+
+  await outputFile(file, str, options)
+}
+
+module.exports = outputJson