fix: security audit - prisma singleton, rate limits, encryption key validation, syntax fixes

src/routes/schemes.ts

@@ -1,11 +1,10 @@
 import { Router, Request, Response } from 'express';
-import { PrismaClient } from '@prisma/client';
 import { z } from 'zod';
 import { authMiddleware, optionalAuth } from '../middleware/auth';
 import { encrypt } from '../utils/encryption';
+import { prisma } from '../utils/prisma';
 
 const router = Router();
-const prisma = new PrismaClient();
 
 // ============================================
 // 获取方案列表