feat: P0生产加固 — 认证安全+操作审计+错误提示

P0-1 认证安全:
- JWT secret 改为环境变量配置, 未设置则随机生成(重启失效)
- 新增 LoginRateLimitMiddleware: 5次/分钟登录频率限制(滑动窗口)
- 429 响应 + 前端 toast 提示

P0-2 操作审计日志:
- 新增 OperationLog 模型 (user/username/action/resource/detail/ip)
- 新增 AuditLogMiddleware 自动记录 POST/PUT/DELETE/PATCH 操作
- 新增 GET /audit-logs API (分页/过滤/统计)
- 前端 AuditLogsPage 对接真实 API (字段/路径修正)

P0-3 实例密码加密:
- 已确认 crypto.py AES-256-GCM 加密存储, 无需修改

P1 前端错误提示:
- 新增 useToast hook + ToastContainer 组件
- request.ts 拦截器: 4xx/5xx 错误 toast 显示后端 detail 信息
- 422 验证错误提取第一条 msg
- 网络失败显示通用提示

1182 tests passed

frontend/src/hooks/useToast.ts

@@ -1,40 +1,33 @@
-import { useState, useEffect, useCallback } from 'react';
-import { CheckCircle, XCircle, X } from 'lucide-react';
+import { useCallback, useState } from 'react';
 
 export interface Toast {
+  id: number;
+  type: 'success' | 'error' | 'warning' | 'info';
   message: string;
-  type: 'success' | 'error';
+}
+
+let toastId = 0;
+let _addToast: ((t: Toast) => void) | null = null;
+
+export function toast(type: Toast['type'], message: string) {
+  if (_addToast) {
+    _addToast({ id: ++toastId, type, message });
+  }
 }
 
 export function useToast() {
-  const [toast, setToast] = useState<Toast | null>(null);
+  const [toasts, setToasts] = useState<Toast[]>([]);
 
-  useEffect(() => {
-    if (!toast) return;
-    const t = setTimeout(() => setToast(null), 3000);
-    return () => clearTimeout(t);
-  }, [toast]);
-
-  const showToast = useCallback((message: string, type: 'success' | 'error' = 'success') => {
-    setToast({ message, type });
+  _addToast = useCallback((t: Toast) => {
+    setToasts(prev => [...prev, t]);
+    setTimeout(() => {
+      setToasts(prev => prev.filter(x => x.id !== t.id));
+    }, 4000);
   }, []);
 
-  const ToastComponent = () => {
-    if (!toast) return null;
-    const isSuccess = toast.type === 'success';
-    return (
-      <div
-        className={`fixed bottom-6 right-6 z-[100] flex items-center gap-2 rounded-lg px-4 py-3 text-sm shadow-lg
-          animate-[fadeInUp_0.25s_ease-out] ${isSuccess ? 'bg-green-500/15 text-green-400' : 'bg-red-500/15 text-red-400'}`}
-      >
-        {isSuccess ? <CheckCircle className="h-4 w-4 shrink-0" /> : <XCircle className="h-4 w-4 shrink-0" />}
-        <span>{toast.message}</span>
-        <button onClick={() => setToast(null)} className="ml-1 hover:opacity-70">
-          <X className="h-3 w-3" />
-        </button>
-      </div>
-    );
-  };
+  const remove = useCallback((id: number) => {
+    setToasts(prev => prev.filter(x => x.id !== id));
+  }, []);
 
-  return { toast, showToast, ToastComponent };
+  return { toasts, remove };
 }