📦 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/fork-ts-checker-webpack-plugin/lib/hooks/pluginHooks.d.ts

@@ -0,0 +1,20 @@
+import * as webpack from 'webpack';
+import { SyncHook, SyncWaterfallHook, AsyncSeriesWaterfallHook } from 'tapable';
+import { FilesChange } from '../reporter';
+import { Issue } from '../issue';
+declare function createForkTsCheckerWebpackPluginHooks(): {
+    start: AsyncSeriesWaterfallHook<FilesChange, webpack.compilation.Compilation, any>;
+    waiting: SyncHook<webpack.compilation.Compilation, any, any>;
+    canceled: SyncHook<webpack.compilation.Compilation, any, any>;
+    error: SyncHook<Error, webpack.compilation.Compilation, any>;
+    issues: SyncWaterfallHook<Issue[], webpack.compilation.Compilation | undefined, void>;
+};
+declare type ForkTsCheckerWebpackPluginHooks = ReturnType<typeof createForkTsCheckerWebpackPluginHooks>;
+declare function getForkTsCheckerWebpackPluginHooks(compiler: webpack.Compiler | webpack.MultiCompiler): {
+    start: AsyncSeriesWaterfallHook<FilesChange, webpack.compilation.Compilation, any>;
+    waiting: SyncHook<webpack.compilation.Compilation, any, any>;
+    canceled: SyncHook<webpack.compilation.Compilation, any, any>;
+    error: SyncHook<Error, webpack.compilation.Compilation, any>;
+    issues: SyncWaterfallHook<Issue[], webpack.compilation.Compilation | undefined, void>;
+};
+export { getForkTsCheckerWebpackPluginHooks, ForkTsCheckerWebpackPluginHooks };