fix: Switch to @fastify/jwt for proper types

backend/package.json

@@ -13,7 +13,7 @@
     "@prisma/client": "^5.7.0",
     "fastify": "^4.25.0",
     "fastify-plugin": "^4.5.0",
-    "fastify-jwt": "^4.2.0",
+    "@fastify/jwt": "^7.2.4",
     "dotenv": "^16.3.1"
   },
   "devDependencies": {

backend/src/server.ts

@@ -1,5 +1,5 @@
 import fastify from 'fastify';
-import jwt from 'fastify-jwt';
+import jwt from '@fastify/jwt';
 import dotenv from 'dotenv';
 import { prismaPlugin } from './plugins/prisma';
 import { authRoutes } from './routes/auth.routes';