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/package-lock.json

@@ -24,6 +24,7 @@
         "zustand": "^4.5.0"
       },
       "devDependencies": {
+        "@types/node": "^26.1.1",
         "@types/react": "^18.3.0",
         "@types/react-dom": "^18.3.0",
         "@vitejs/plugin-react": "^4.3.0",
@@ -1309,6 +1310,16 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@types/node": {
+      "version": "26.1.1",
+      "resolved": "https://registry.npmmirror.com/@types/node/-/node-26.1.1.tgz",
+      "integrity": "sha512-nxAkRSVkN1Y0JC1W8ky/fTfkGsMmcrRsbx+3XoZE+rMOX71kLYTV7fLXpqud1GpbpP5TuffXFqfX7fH2GgZREw==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "undici-types": "~8.3.0"
+      }
+    },
     "node_modules/@types/pako": {
       "version": "2.0.4",
       "resolved": "https://registry.npmmirror.com/@types/pako/-/pako-2.0.4.tgz",
@@ -3303,6 +3314,13 @@
         "node": ">=14.17"
       }
     },
+    "node_modules/undici-types": {
+      "version": "8.3.0",
+      "resolved": "https://registry.npmmirror.com/undici-types/-/undici-types-8.3.0.tgz",
+      "integrity": "sha512-j375ScV60dom+YkPFIfTLcOiPxkN/buHz5GobjLhixFuANaNs3C9l4GmrWqejgXWJ7BbJcFYpTEUkS1Ge8bpZQ==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/update-browserslist-db": {
       "version": "1.2.3",
       "resolved": "https://registry.npmmirror.com/update-browserslist-db/-/update-browserslist-db-1.2.3.tgz",