fix: 修复前后端编译警告 — 移除未使用变量/导入/函数

前端:
- 移除未使用导入: FileText, AlertCircle, RefreshCw, Signal, QrCode, Upload, Save, Bell, History, useMemo, Select
- 移除未使用变量/函数: scope, cfg, org, paged, salaryNum, ackColor, resultColor, maxEmployees, compareVersions, showRenewPreview, showEvidence, handleStartDateChange, ResultRow, previewEmployeeId, updateMutation
- 修复 vite.config.ts: 安装 @types/node 并配置 tsconfig.node.json
- 将未使用参数 req/s 改为 _req/_s

后端:
- 移除未使用导入: Request, Response, NextFunction, decrypt, ContractType, ensureDefaultTemplate
- 移除未使用变量/常量: scope, cfg, org, orgId(preview), monthNum, TAX_BRACKETS, months, daysBetween
- 将未使用参数 req 改为 _req

frontend/vite.config.js

@@ -0,0 +1,20 @@
+import { defineConfig } from 'vite';
+import react from '@vitejs/plugin-react';
+import path from 'path';
+export default defineConfig({
+    plugins: [react()],
+    resolve: {
+        alias: {
+            '@': path.resolve(__dirname, './src'),
+        },
+    },
+    server: {
+        port: 5173,
+        proxy: {
+            '/api': {
+                target: 'http://localhost:3000',
+                changeOrigin: true,
+            },
+        },
+    },
+});